Document recommendations for frameworks using Hydra

Create a page that will help putting framework owners on the right path.

Explain the two involved spaces:

• config paths (relative to the search path) : shared space with other INSTALLED apps and frameworks. not flexible (not be changed once an app is installed):
• config packages: normally lines up with the config path, but is flexible and can be overridden via package overrides.

Other things to explain:

1. The role of a config source plugin for frameworks.
2. The role of SearchPathPlugins
3. anything else?

Edit: added hyperlinks - Jasha