Adding initial CONTRIBUTING.md
Changing pull request to PR.
Making repo rights explicit for core contributors.
Breaking up core contributor change process into smaller bullet points.
Adjust all headings except first one to be h2.
Clarifying where to specify +1; emphasizing "any".
Fixing links to anchors on same page.
Adding rationale.
Fixing from/to order to read better (IMO).
Clarifying which list to change.
s/repo/repository/
Fixing typo.
Clarifying - change to what?
Adding definitions for some design decisions.
Removing 7-day self-merge clause.
Merge pull request #1 from ycombinator/dev

Adding initial CONTRIBUTING.md