Improve configuration documenation

[nharlow89]

As a new user to this package, I have had a difficult time digging through the serverless docs trying to figure out which arguments and configurations are available. There are many incomplete or trivial examples scattered throughout the docs, and many configurations that are not compatible with the google provider. What would be most helpful is a complete list of available properties for Google Cloud deployments specifically. In other words, this page but for the google provider: https://www.serverless.com/framework/docs/providers/aws/guide/serverless.yml/