docs: update developer docs to use geminicli GCS bucket (#13)

Author: twishabansal

DEVELOPER.md

@@ -37,7 +37,7 @@ The core logic for this extension is handled by a pre-built `toolbox` binary. Th
     # Download the binary for your platform. The binary must be named `toolbox`.
     # Adjust the URL for your operating system (`linux/amd64`, `darwin/arm64`, `windows/amd64`).
     # Example for macOS/amd64:
-    curl -L -o toolbox https://storage.googleapis.com/genai-toolbox/v$VERSION/darwin/amd64/toolbox
+    curl -L -o toolbox https://storage.googleapis.com/genai-toolbox/geminicli/v$VERSION/darwin/amd64/toolbox
     chmod +x toolbox
 
     # For Windows, you will need to download the .exe file and rename it to `toolbox`.