Walk through the "Saving data" in gcloud.datastore's Docs?

[jgeewax]

Looks like it's not 100% clear to people how they can save data of different types. Maybe we should write some better documentation in the overview page explaining common tasks you want to do with Datastore? (Reference: #553)

/cc @ryanseys

[ryanseys]

Assigning to myself to take a look at making these better.

[ryanseys]

@jgeewax Does this suffice or would you like something more?

[jgeewax]

LGTM