Make sure gcloud-auth doc isn't too datastore specific

[dhermes]

From @tseaver in: https://github.com/GoogleCloudPlatform/gcloud-python/pull/1137/files#r39682019

Dunno -- maybe it just needs to note that the other API clients are all similar (actually, datastore is the oddball, compared to storage/pubsub/bigquery/dns).

[dhermes]

@tseaver The only mention of datastore is at the beginning in the "Client-Provided Authentication" section:

Nothing else even mentions a sub-package (though we do later mention all the services and required scopes).

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I can change it if you like, what do you think would work better?

I know I've got to send a PR against this doc since I discovered that we've got broken links:
https://raw.githubusercontent.com/GoogleCloudPlatform/gcloud-common/master/authorization/enable-apis.png
has become
https://raw.githubusercontent.com/GoogleCloudPlatform/gcloud-common/master/authentication/enable-apis.png
(and similar for the other 2 or 3 such images we use in this doc).

(I caused this since I asked the node guys and gcloud-common to say authentication instead of authorization.)

[dhermes]

@tseaver Bump

[tseaver]

Works for me. I must have been bleary-eyed.

[dhermes]

Closing now. (Only left it open until I remembered to do the work in #1166)