R1:b3d8ea88ecad

Update a couple of links in "Feature Requests" documentation

Summary:
These are a little out of date:

- Link to Starmap since it explicitly exists now.
- Link to "Planning" instead of the old task.
- Link to "Prioritization" instead of telling anyone to build stuff themselves.

Test Plan: Read documentation.

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D14328