Update README.md (#50)

Author: Smetalo

README.md

@@ -99,7 +99,7 @@ The Security extension scans files for the following vulnerabilities:
 
 ## Resources
 
-- [Gemini CLI extensions](https://github.com/google-gemini/gemini-cli/blob/main/docs/extension.md): Documentation about using extensions in Gemini CLI
+- [Gemini CLI extensions](https://github.com/google-gemini/gemini-cli/blob/main/docs/extensions/index.md): Documentation about using extensions in Gemini CLI
 - Blog post (coming soon!): More information about the Security extension
 - [GitHub issues](https://github.com/gemini-cli-extensions/security/issues): Report bugs or request features