Update the README to follow the new format

[jgeewax]

See https://github.com/GoogleCloudPlatform/gcloud-meta/issues/3 for what we're hoping to be the shared (mostly) format.

• builds/pypi/coveralls
• services supported
• quickstart
• example applications
• authorization
• example of bigquery (longer)
• example of datastore (longer)
• example of storage (longer)
• Example: datastore - Dataset#save
• contributing
• license

[ryanseys]

I've added a checkbox list based on the meta-link. Authorization could use some code snippets but how much longer do the examples need to be and what would we like to specifically show off that we aren't currently showing off?

[ryanseys]

Added authorization clarifications to README. I'd say we are done with this as our examples seem sufficient. @stephenplusplus thoughts?

[stephenplusplus]

I'd agree that it all looks good to me. I think the only other thing that could be useful is showing dataset.save, as that seems to be the one "big" use missing.

[ryanseys]

I think we are good here. Feel free to re-open if you have more ideas for how we can improve the README.