docs: add comments to craft-options in craft.yml

Document craft-options based on static-php-cli documentation: doctor
checks the environment, download fetches php-src and libraries, and
build compiles the static binary.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: pjcdawkins

ext/craft.yml

@@ -27,6 +27,6 @@ download-options:
   retry: 5
 
 craft-options:
-  doctor: true
-  download: true
-  build: true
+  doctor: true    # Check environment and automatically fix when possible.
+  download: true  # Download source code (php-src and libraries).
+  build: true     # Build the static PHP binary.