Update README.md

Author: averikitsch

README.md

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 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, and explore schemas directly from the [Gemini CLI](https://google-gemini.github.io/gemini-cli/), using natural language prompts.
 enhance the user experience by providing a unified interface for managing and monitoring database performance and health by letting the customers get the system/query insights data via Gemini CLI.
 
-Learn more about [Gemini CLI Extensions](https://github.com/google-gemini/gemini-cli/blob/main/docs/extension.m
+Learn more about [Gemini CLI Extensions](https://github.com/google-gemini/gemini-cli/blob/main/docs/extension.md)
 
 ## Why Use the Cloud SQL for PostgreSQL Observability Extension?