docs: update Learning Hub for CLI v1.0.6–v1.0.10 changes (#1119)

- automating-with-hooks: add subagentStart event to hook events table,
  add cross-platform PascalCase event name compatibility note, add
  subagentStart example, expand hook config file location FAQ to include
  settings.json and config.json locations
- defining-custom-instructions: document that applyTo accepts both
  string and array formats (added in v1.0.6)
- installing-and-using-plugins: document --plugin-dir flag and the
  External Plugins section in /plugin list (added in v1.0.10)

Source: github/copilot-cli releases v1.0.6 through v1.0.10
(March 16–20, 2026)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

website/src/content/docs/learning-hub/defining-custom-instructions.md

@@ -3,7 +3,7 @@ title: 'Defining Custom Instructions'
 description: 'Learn how to create persistent, context-aware instructions that guide GitHub Copilot automatically across your codebase.'
 authors:
   - GitHub Copilot Learning Hub Team
-lastUpdated: 2025-12-02
+lastUpdated: 2026-03-22
 estimatedReadingTime: '8 minutes'
 tags:
   - instructions
@@ -100,7 +100,17 @@ export function UserProfile({ userId, onUpdate }: UserProfileProps) {
 
 ## Scoping Instructions Effectively
 
-The `applyTo` field determines which files receive the instruction's guidance.
+The `applyTo` field determines which files receive the instruction's guidance. It accepts either a **comma-separated string** or an **array of glob patterns** — both formats work:
+
+```yaml
+# String format (comma-separated)
+applyTo: '**/*.ts, **/*.tsx'
+
+# Array format
+applyTo:
+  - '**/*.ts'
+  - '**/*.tsx'
+```
 
 ### Common Scoping Patterns