content for definition-of-ready

[charleszipp]

This is for the new proposed outline in #53

This content should define the criteria a team should use to determine if a story is ready to pull into a sprint. Example is, team understands the implementation, how to prove work meets acceptance, estimated, etc.

[fnocera]

To be added here https://github.com/microsoft/code-with-engineering-playbook/tree/master/team-agreements/definition-of-ready