Add more documentation on cron, Datastore, and Cloud Storage
Add more documentation on cron, Datastore, and Cloud Storage

Note that a lot of this is adapted from existing non-Markdown documentation written by Brian.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=129252200

google/nomulus,google/nomulus,google/nomulus,google/nomulus,google/nomulus,google/nomulus