Add validation guide for query-pack change notes

Added a validation guide for query-pack change notes, including file naming conventions, frontmatter requirements, and examples of valid and invalid entries.

Author: mario-campos

.github/instructions/query-pack-change-notes.instructions.md

@@ -0,0 +1,116 @@
+---
+applyTo: >
+  actions/ql/src/change-notes/*.md,
+  cpp/ql/src/change-notes/*.md,
+  csharp/ql/src/change-notes/*.md,
+  go/ql/src/change-notes/*.md,
+  java/ql/src/change-notes/*.md,
+  javascript/ql/src/change-notes/*.md,
+  python/ql/src/change-notes/*.md,
+  ql/ql/src/change-notes/*.md,
+  ruby/ql/src/change-notes/*.md,
+  rust/ql/src/change-notes/*.md,
+  swift/ql/src/change-notes/*.md
+---
+
+# Validation guide for query-pack change notes
+
+When performing a code review, ensure that the Markdown change-notes in the pull request meet the following standards:
+
+## File name
+The file name must match this pattern: `YYYY-MM-DD-description.md`
+- `YYYY-MM-DD` should refer to the year, month, and day, respectively, of the change;
+- `description` should refer to a short alphanumerical text, separated by hyphens, that describes the change-note;
+- The extension should be ".md".
+
+### Examples
+#### Valid
+
+- 2020-10-12-new-client-library.md
+- 2025-01-01-refactored-database-logic.md
+- 2022-12-25-removed-log4j.md
+
+#### Invalid
+
+- 3000-60-32-invalid-date.md
+- no-date-in-file-name.md
+- 2019-01-01 file name contains spaces.md
+
+## Frontmatter
+The file must begin with YAML frontmatter. Valid YAML frontmatter properties include:
+
+- `category`
+  - Required
+  - This is a string that identifies one of a fixed set of categories that the change falls into.
+- `tags`
+  - Optional
+  - A list of string tags.
+
+### Categories
+| Category         | Description |
+|------------------|-------------|
+| `breaking`       | Any breaking change to the query pack, the most common of which is the deletion of an existing query. |
+| `deprecated`     | An existing query has been marked as `deprecated`. |
+| `newQuery`       | A new query has been added. |
+| `queryMetadata`  | The metadata of a query has been changed (e.g., to increase or reduce the `@precision`). |
+| `majorAnalysis`  | The set of results produced by a query has changed (fewer false positives, more true positives, etc.) enough to be noticed by users of the query pack. |
+| `minorAnalysis`  | The set of results produced by a query has changed, but only in scenarios that affect relatively few users. |
+| `fix`            | A fix that does not change the results reported by a query (e.g., a performance fix). |
+
+### Examples
+#### Valid
+
+```yaml
+---
+category: newQuery
+---
+```
+
+```yaml
+---
+category: majorAnalysis
+tags: cpp
+---
+```
+
+#### Invalid
+
+##### Missing `category` property
+
+```yaml
+---
+tags: cpp
+---
+```
+
+##### Invalid category `bug`; use `fix` instead
+
+```yaml
+---
+category: bug
+---
+```
+
+## Description
+The content after the YAML frontmatter must be an American-English description of the change in one or more unordered Markdown list entries.
+
+### Examples
+
+#### Valid
+
+```markdown
+* Added support for the Nim programming language.
+```
+
+#### Invalid
+
+##### Change description is not in a bullet-list entry
+```markdown
+Added support for the Nim programming language.
+```
+
+##### No headers; only list entries
+```markdown
+# Fixes
+* Fixed C++ source parsing to handle comma operator.
+```