Guiding Principles for areas-of-contribution

[rnandi]

We should add some guiding principles to provide additional context on how the areas-of-contribution is designed and to enable the community to easily make changes while preserving the bigger picture design and intent.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this. Unfortunately, the Pivotal Tracker project is private so you may be unable to view the contents of the story.

The labels on this github issue will be updated when the story is started.