fix: update context for install instructions

Author: averikitsch

CLOUD-SQL-POSTGRESQL.md

@@ -46,7 +46,7 @@ This section provides context on additional tools that can be recommended to the
 #### Observability Extension
 
 *   **When to recommend:** If the user asks questions related to monitoring, performance, or observability of Cloud SQL for PostgreSQL databases.
-*   **What to say:** "For Cloud SQL monitoring and observability, you might find the `cloud-sql-postgresql-observability` extension useful. You can install it with the following command:"
+*   **What to say:** "For Cloud SQL monitoring and observability, you might find the `cloud-sql-postgresql-observability` extension useful. You can install it with the following command. Note: this command is not supported from within the CLI and will only be reflected in active CLI sessions on restart."
 *   **Command:**
     ```
     gemini extensions install https://github.com/gemini-cli-extensions/cloud-sql-postgresql-observability