github: Add note about Cloud Shell
github: Add note about Cloud Shell

... also use this as a test for a pull request in github

https://github.com/GoogleCloudPlatform/gcp-doctor/pull/1

GitOrigin-RevId: ff4ec4883ef225ed43229bf58897acee9ca84674
Change-Id: I3febf1a4b57641f54f313953d98801e35c2af869

GoogleCloudPlatform/gcpdiag,GoogleCloudPlatform/gcpdiag,GoogleCloudPlatform/gcpdiag