docs: add cli demo for gemini extension and mcp server

Author: jpoehnelt

docs/gemini.tape

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+Output gemini.gif
+
+Set Width 1920
+Set Height 1080
+
+Set PlaybackSpeed 1
+
+Hide
+Type "source .env"
+Enter
+Sleep 1s
+Type " gemini extensions uninstall google-workspace-developer-tools"
+Enter
+Sleep 1s
+Type "clear"
+Enter
+Sleep 1s
+Show
+
+Type "gemini extensions install https://github.com/googleworkspace/developer-tools"
+Sleep 200ms
+Enter
+Sleep 2s
+Type "Y"
+Sleep 200ms
+Enter
+Sleep 2s
+
+Type "gemini"
+Sleep 200ms
+Enter
+Sleep 5s
+
+Ctrl+t
+Sleep 1s
+
+Type "Tell me about Apps Script using the search_workspace_docs tool."
+Sleep 200ms
+Enter
+Sleep 5s
+Enter # Allow tool usage
+Sleep 20s
+
+Type "/quit"
+Sleep 200ms
+Enter
+Sleep 3s