config (#171): add PR template to prevent PRs at the moment

Author: bencodezen

.github/pull_request_template.md

@@ -0,0 +1,7 @@
+## Note
+
+Thanks for your interest in submitting a PR! At this time, because the docs are in beta, the team is currently in the midst of changes and we are not ready for additional contributions yet.
+
+To bring your issue to the team's attention though, we would recommend [creating an issue](https://github.com/vuejs/docs-next/issues/new) and we'll get to it when we can.
+
+Thanks for your understanding!