Update src/release-notes/README.md (#58840)

Author: heiskr

src/release-notes/README.md

@@ -1,3 +1,69 @@
-# Release notes
+# Release Notes
 
-Our release notes pages are specific to GitHub Enterprise Server (GHES). These pages list the change contained in each version of GHES.
+This module manages the fetching, processing, and rendering of GitHub Enterprise Server (GHES) release notes. These notes are displayed on dedicated pages (e.g., `/en/enterprise-server@3.19/admin/release-notes`) and list the features, bug fixes, and known issues for each patch release.
+
+## Purpose & Scope
+
+The primary goal is to:
+- **Parse Release Data**: Read structured YAML data containing release notes.
+- **Format & Sort**: Organize notes by version (major.minor) and patch level.
+- **Render Content**: Process Markdown and Liquid within the notes.
+- **Contextualize**: Inject the processed notes into the page context for rendering by React components.
+
+## Architecture
+
+### Data Source
+
+Release notes are stored in the `data/release-notes/enterprise-server` directory.
+- **Origin**: The content is sourced externally and synced to this repository.
+- **Format**: YAML files organized by version.
+- **Structure**: Each file contains entries for patch releases, including sections for "Features", "Bugs", "Security", etc.
+
+### Middleware
+
+The core logic resides in `src/release-notes/middleware/ghes-release-notes.ts`.
+- **Route Detection**: It activates only for GHES release notes pages or the Admin landing page.
+- **Data Retrieval**: Fetches raw data using `getReleaseNotes`.
+- **Forced English**: Currently, it forces the content language to English (`en`) during rendering. This is a workaround because the source Markdown often lacks Liquid variables for product names, leading to undesirable translations of proper nouns (e.g., "GitHub Copilot" becoming translated literally).
+- **Rendering**: Uses `renderPatchNotes` to process the Markdown/Liquid content of each note.
+
+### Library
+
+`src/release-notes/lib/release-notes-utils.ts` provides helper functions:
+- **`formatReleases`**: Sorts releases and patches semantically (using `semver`). It transforms the raw data into a structured array suitable for the UI.
+- **`renderPatchNotes`**: Iterates through sections (features, bugs, etc.) and renders the content strings.
+
+### Components
+
+The frontend rendering is handled by React components in `src/release-notes/components`:
+- **`GHESReleaseNotes.tsx`**: The main container.
+- **`PatchNotes.tsx`**: Renders the details of a specific patch.
+
+## Maintenance
+
+### Sourcing
+
+Release notes are received from an external source. **Do not manually create or edit release note files in this repository** unless specifically instructed to do so by the release process or for testing purposes.
+
+The files in `data/release-notes` are the destination for this external data.
+
+### URL Structure
+
+- **Page**: `/en/enterprise-server@<version>/admin/release-notes`
+- **Anchor**: `#3.19.1` (Links to specific patch notes)
+
+## Dependencies
+
+- **`semver`**: Used for sorting and comparing version strings.
+- **`src/versions`**: Used to determine supported GHES versions (`latestStable`, `all`).
+- **`src/content-render`**: Used to render the Markdown content within the notes.
+
+## Ownership
+
+- **Team**: `@github/docs-engineering`
+- **Content Owners**: The Writers and Release Managers responsible for the GHES release process.
+
+## Current State & Known Issues
+
+- **Translation Workaround**: As mentioned, we currently force English rendering for release notes to avoid "over-translation" of product names. This is a known limitation until the source data is updated to use proper Liquid variables.
+- **Legacy Redirects**: The middleware handles redirects for very old versions (pre-2.20) to `enterprise.github.com`.