chore: Update ReadMe disclaimer (#15)

Co-authored-by: Wenxin Du <117315983+duwenxin99@users.noreply.github.com>

Author: averikitsch

README.md

@@ -1,7 +1,7 @@
 # Gemini CLI Extension - Cloud SQL for SQL Server
 
 > [!NOTE]
-> This extension is currently in beta, and may see breaking changes until the first stable release (v1.0).
+> This extension is currently in beta (pre-v1.0), and may see breaking changes until the first stable release (v1.0).
 
 This Gemini CLI extension provides a set of tools to interact with [Cloud SQL for SQL Server](https://cloud.google.com/sql/docs/sqlserver) 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.