docs: update readme getting started instructions (#29)

* docs: update readme getting started instructions

* Update README.md

Co-authored-by: Yuan Teoh <45984206+Yuan325@users.noreply.github.com>

---------

Co-authored-by: Yuan Teoh <45984206+Yuan325@users.noreply.github.com>

Author: averikitsch

README.md

@@ -23,15 +23,17 @@ Before you begin, ensure you have the following:
     * Cloud Spanner Database Reader (`roles/spanner.databaseReader`)
     * Cloud Spanner Database User (`roles/spanner.databaseUser`)
 
-## Installation
+## Getting Started
+
+### Installation
 
 To install the extension, use the command:
 
 ```bash
 gemini extensions install https://github.com/gemini-cli-extensions/spanner
 ```
 
-## Configuration
+### Configuration
 
 Set the following environment variables before starting the Gemini CLI:
 
@@ -42,6 +44,19 @@ Set the following environment variables before starting the Gemini CLI:
 
 Ensure [Application Default Credentials](https://cloud.google.com/docs/authentication/gcloud) are available in your environment.
 
+### Start Gemini CLI
+
+To start the Gemini CLI, use the following command:
+
+```bash
+gemini
+```
+
+> [!WARNING]
+> **Changing Instance & Database Connections**
+> Currently, the database connection must be configured before starting the Gemini CLI and can not be changed during a session.
+> To save and resume conversation history use command: `/chat save <tag>` and `/chat resume <tag>`.
+
 ## Usage
 
 *   **Explore Schemas and Data:**
@@ -64,4 +79,6 @@ Find additional extensions to support your entire software development lifecycle
 
 ## Troubleshooting
 
-* "cannot execute binary file": Ensure the correct binary for your OS/Architecture has been downloaded. See [Installing the server](https://googleapis.github.io/genai-toolbox/getting-started/introduction/#installing-the-server) for more information.
+* "✖ Error during discovery for server: MCP error -32000: Connection closed": The database connection has not been established. Ensure your configuration is set via environment variables.
+* "✖ MCP ERROR: Error: spawn /Users/<USER>/.gemini/extensions/spanner/toolbox ENOENT": The Toolbox binary did not download correctly. Ensure you are using Gemini CLI v0.6.0+.
+* "cannot execute binary file": The Toolbox binary did not download correctly. Ensure the correct binary for your OS/Architecture has been downloaded. See [Installing the server](https://googleapis.github.io/genai-toolbox/getting-started/introduction/#installing-the-server) for more information.