Update CONTRIBUTING.md and add install instructions to README.md

CONTRIBUTING.md

@@ -1 +1,114 @@
-See Crossplane's [contributing](https://github.com/crossplane/crossplane/tree/main/contributing).
+# Contributing to the Crossplane CLI
+
+Welcome to the Crossplane CLI, and thank you for your interest in contributing.
+
+Please start by reading the [Crossplane contributing document]. The Crossplane
+CLI follows the same guidelines and policies as the core Crossplane project,
+including coding style. We also use a similar Nix-based development environment.
+
+The CLI maintainers primarily communicate in the [#sig-cli] channel on Slack.
+
+Topics specific to CLI development are covered below.
+
+## The Command Tree
+
+The Crossplane CLI's command tree follows a noun-first structure. This means all
+top-level commands are nouns (`cluster`, `composition`, `dependency`) rather
+than verbs (`get`, `list`, `generate`). New commands should be added under the
+relevant noun, or a new noun if needed. Please feel free to ask on Slack or
+propose a new command in an issue if you aren't sure where a new command should
+go.
+
+## kong
+
+We use [kong] as our CLI framework. Each command is defined as a struct, in
+which fields become subcommands, positional arguments, or flags. Kong's [struct
+tags] can be used to control many behaviors, including validation,
+auto-completion, and documentation.
+
+## Command Maturity Levels
+
+We have three maturity levels for commands:
+
+- Generally Available (GA): Stable commands that will not be removed or have
+  breaking changes made without considerable notice.
+- Beta: Commands that are relatively stable and unlikely to be removed, but may
+  have breaking changes made in a subsequent minor version.
+- Alpha: Experimental commands that may change significantly or be removed at
+  any time.
+
+Alpha and beta commands are marked as such using a custom kong struct tag,
+`maturity:"alpha"` or `maturity:"beta"`. These struct tags control two things:
+
+1. Alpha commands are hidden from the help output by default. Users must enable
+   showing alpha commands in their CLI configuration file.
+2. Alpha and beta commands automatically have notes added to their help text
+   indicating the maturity level and what it means.
+
+Note that in the past alpha and beta commands were put under separate command
+trees (`crossplane alpha` and `crossplane beta`). We have moved away from this
+scheme in order to help keep the command tree and codebase more stable as
+commands mature.
+
+## Embedded Documentation
+
+The CLI is self-documenting. Short descriptions for commands and flags should be
+added using kong struct tags. Longer help should be returned by each command's
+`Help()` method. This help should be formatted using markdown, which we render
+in the console using the [glamour] library.
+
+The `crossplane generate-docs` command is used to generate CLI reference
+documentation for [docs.crossplane.io]. Markdown returned by each command's
+`Help()` is embedded nearly verbatim into this documentation. Please observe the
+following guidelines in order to make the docs look as good as possible:
+
+- Don't put a top-level heading on your Markdown-formatted detailed help. An
+  appropriate heading will be added automatically in both terminal usage and
+  docs generation.
+- Use level 2 headings (`##`) and below for sections in your help text. These
+  will render correctly in the terminal, and be adjusted as needed by the
+  `generate-docs` command to ensure the documentation page is properly
+  structured.
+- Use inline code and code blocks for commands, flags, arguments, etc. This
+  looks good when rendered, and avoids spelling and grammar false positives.
+
+If in doubt about whether your help will look good, you can easily check your
+work by cloning the [crossplane/docs](https://github.com/crossplane/docs) repo,
+running `crossplane generate-docs -o content/master/cli/command-reference.md` to
+update the CLI reference section, and then running `hugo serve` to preview it
+locally.
+
+### The `vale` Linter
+
+The Crossplane documentation uses [vale] to enforce spelling and style
+guidelines. This repository includes a CI check that generates documentation and
+runs `vale` using the configuration from [crossplane/docs] to ensure that our
+generated documentation does not trigger any warnings or errors.
+
+It is sometimes unavoidable to have help text that triggers vale warnings or
+errors. For example, the heading for the help section about the `crossplane
+config` command includes the word "config" outside a code block, causing vale to
+suggest that we replace it with "configuration". For these situations, it is
+possible to temporarily disable specific vale rules in two ways:
+
+1. If the problem is in detailed Markdown help, use [vale Markdown comments].
+2. If the problem is in help generated by kong (command names, flag
+   descriptions, etc.), use our custom `novale:"..."` kong tag. This will result
+   in a Markdown comment of the form `<!-- vale ... = NO -->` being generated at
+   the top of the relevant command's documentation section with a matching `=
+   YES` comment at the bottom.
+
+In both cases, please scope vale overrides as tightly as possible and ensure all
+rules are re-enabled after the problematic section. Prefer to disable specific
+matches rather than whole rules, and rules rather than whole styles.
+
+<!-- Named links -->
+
+[Crossplane contributing document]: https://github.com/crossplane/crossplane/tree/main/contributing
+[#sig-cli]: https://crossplane.slack.com/archives/C08V9PMLRQA
+[kong]: https://pkg.go.dev/github.com/alecthomas/kong
+[struct tags]: https://pkg.go.dev/github.com/alecthomas/kong#readme-supported-tags
+[glamour]: https://pkg.go.dev/github.com/charmbracelet/glamour
+[docs.crossplane.io]: https://docs.crossplane.io/latest/cli/command-reference/
+[vale]: https://vale.sh
+[vale Markdown comments]: https://vale.sh/docs/formats/markdown#comments

README.md

@@ -8,6 +8,37 @@ platforms on top of Crossplane and working with Crossplane clusters.
 
 Crossplane is a [Cloud Native Computing Foundation][cncf] project.
 
+## Installation
+
+The Crossplane CLI is a single binary, which we build for macOS, Linux, and
+Windows. You can download the latest version using the install script:
+
+```shell
+curl -sfL "https://cli.crossplane.io/install.sh" | sh
+```
+
+The script detects your operating system and CPU architecture and downloads the
+appropriate binary to the current directory. Note that it does not attempt to
+place the binary in your shell's `$PATH`, so you may want to move it.
+
+To install a different version of the CLI, set `XP_VERSION` when running the
+install script:
+
+```shell
+curl -sfL "https://cli.crossplane.io/install.sh" | XP_VERSION=v2.3.1 sh
+```
+
+To install the latest build from our main branch, set `XP_CHANNEL=master`:
+
+```shell
+curl -sfL "https://cli.crossplane.io/install.sh" | XP_CHANNEL=master sh
+```
+
+## Reference Documentation
+
+Command reference documentation for the CLI can be found on
+[docs.crossplane.io](https://docs.crossplane.io/latest/cli/command-reference/).
+
 ## License
 
 Crossplane is under the Apache 2.0 license.