Move Claude Code plugin docs under Installation section

Author: fprochazka

README.md

@@ -52,15 +52,11 @@ glab-discussion resolve DISCUSSION_ID --mr-url ...
 glab-discussion resolve DISCUSSION_ID --unresolve --mr-url ...
 ```
 
-## Claude Code plugin
+### Claude Code plugin
 
 The repo includes a Claude Code plugin with a skill that teaches AI agents how to use `glab-discussion`.
 
 ```bash
-# Install the CLI
-uv tool install glab-discussion
-
-# Add the marketplace and install the plugin
 claude plugin marketplace add fprochazka/glab-discussion
 claude plugin install glab-discussion@fprochazka-glab-discussion
 ```