docs: add indexing performance notes to CLAUDE.md

Document expected indexing times so appropriate timeouts are used:
- nixos-options: ~5-6 minutes for nixos-unstable
- hm-options: ~1-2 minutes for master

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -223,3 +223,10 @@ nix run .#hm-options -- serve
 nix run .#nixos-options -- index nixos-unstable
 nix run .#hm-options -- index hm-unstable
 ```
+
+### Indexing Performance
+Indexing operations are slow due to Nix evaluation and file downloads. When running index commands, use appropriate timeouts:
+- **nixos-options**: ~5-6 minutes for `nixos-unstable` (with files)
+- **hm-options**: ~1-2 minutes for `master` (with files)
+
+Use `--no-files` flag for faster indexing (~1-2 minutes) if file content lookup isn't needed.