chore: Update README.md (gemini-cli-extensions#34)

Author: Smetalo

README.md

@@ -5,7 +5,7 @@
 
 This Gemini CLI extension provides a set of tools to interact with [Cloud SQL for PostgreSQL](https://cloud.google.com/sql/docs/postgres) instances. It allows you to manage your databases, execute queries, explore schemas, and troubleshoot issues directly from the [Gemini CLI](https://google-gemini.github.io/gemini-cli/), using natural language prompts.
 
-Learn more about [Gemini CLI Extensions](https://github.com/google-gemini/gemini-cli/blob/main/docs/extension.md).
+Learn more about [Gemini CLI Extensions](https://github.com/google-gemini/gemini-cli/blob/main/docs/extensions/index.md).
 
 ## Why Use the Cloud SQL for PostgreSQL Extension?