While the general policy of not taking changes to the project via pull
requests directly on GitHub has not changed, it can be useful to submit
a PR there in order to trigger a CI run on Azure.  These are run
automatically and the results are populated back to GitHub.  Add a note
to the template to reflect this.

Signed-off-by: Tom Rini <trini@konsulko.com>

On our mirror account on github we have gotten a handful of pull
requests.  At this time github does not allow you to disable pull
requests on a project.  The generally suggested work-around is to add a
pull request template that tells people to not use that workflow.  Add
one here that points to the wiki page on submitted patches.

Signed-off-by: Tom Rini <trini@konsulko.com>