github: Add a PR template to help new users

Hopefully this addresses the most common things.

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,27 @@
+## Tips:
+
+* commit message titles must be in the form:
+```topic: Capitalized message with no trailing period```
+or:
+```topic, topic2: Capitalized message with no trailing period```
+
+* please rebase your patch against current git master:
+```
+git checkout master
+git pull origin master
+git checkout your-feature
+git rebase master
+git push your-remote your-feature
+hub pull-request	# or submit with the github web ui
+```
+
+* after a patch review, please ping @purpleidea so we know to re-review:
+```
+# make changes based on reviews...
+git add -p		# add new changes
+git commit --amend	# combine with existing commit
+git push your-remote your-feature -f
+# now ping @purpleidea in the github PR since it doesn't notify us automatically
+```
+
+## Thanks for contributing to mgmt and welcome to the team!