document GCS authentication

[petedannemann]

document GCS authentication

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[mpenkov]

Good start. Left you some comments. Please check them out.

[petedannemann]

@mpenkov thanks for the review. I addressed your comments

[mpenkov]

Very good. Could you please add links to Google's documentation about where you can get this JSON and token? It would be a great help to people unfamiliar with GCS, like me, when they first try to play around with it.

[petedannemann]

Sure thing, I just added that to the docs.

[mpenkov]

Very good. Thank you!