chore: Update README.md (gemini-cli-extensions#27)

Author: Smetalo

README.md

@@ -5,7 +5,7 @@
 
 This Gemini CLI extension provides a set of tools to interact with [Cloud SQL for SQL Server](https://cloud.google.com/sql/docs/sqlserver)  monitoring metrics. It allows you to fetch a wide range of database metrics, enabling comprehensive monitoring of database performance and health 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 SQL Server Observability Extension?