With PR #7568 we'll have at least four files that someone wanting to contribute to the AMP Project might look at--CONTRIBUTING.md, DEVELOPING.md and the two new guides. We should clean up the redundancies between these files and make it more clear to new and ongoing contributors where they should look for information.

I've also found that DEVELOPING.md has a lot of details that may only be relevant in certain situations without clearly indicating when it would be useful (e.g. SauceLabs, A4A Envelope). We should figure out the best way of presenting this information.