docs(comment-checker): document local installer

Author: code-yeongyu

README.md

@@ -67,9 +67,10 @@ From the marketplace root containing this plugin:
 
 ```bash
 codex plugin marketplace add /path/to/codex-plugins
+node /path/to/codex-plugins/scripts/install-local.mjs /path/to/codex-plugins
 ```
 
-If your local Codex build does not yet expose `codex plugin add`, install from the UI or copy the plugin into `~/.codex/plugins/cache/<marketplace>/codex-comment-checker/0.1.0` and enable:
+If your local Codex build exposes plugin install commands, you can install from the UI or CLI instead. For older local builds, the marketplace installer builds and copies the plugin into `~/.codex/plugins/cache/<marketplace>/codex-comment-checker/0.1.0`, installs runtime dependencies there, and enables:
 
 ```toml
 [plugins."codex-comment-checker@code-yeongyu-codex-plugins"]