GitHub Pull Request template to discourage folks from making PRs
GitHub Pull Request template to discourage folks from making PRs

Simple pull request template encouraging potential contributors
to submit via ReviewBoard instead of opening up a PR on GitHub.

Normally I wouldn't want to add something to the repo that is
platform specific, but given the fact that we have a lot of exposure
on GitHub and that there's no way to disallow PRs, it might be a
good idea to point potential contributors in the right direction
from the get go.

Reviewed at https://reviews.apache.org/r/65222/

rdelval/aurora,thinker0/aurora,medallia/aurora,medallia/aurora,medallia/aurora,rdelval/aurora,medallia/aurora,apache/aurora,apache/aurora,rdelval/aurora,rdelval/aurora,rdelval/aurora,apache/aurora,thinker0/aurora,thinker0/aurora,rdelval/aurora,thinker0/aurora,medallia/aurora,thinker0/aurora,apache/aurora,thinker0/aurora,apache/aurora,apache/aurora,medallia/aurora