add pull request template to try to discourage wrong PRs

Author: daattali

.github/pull_request_template.md

@@ -0,0 +1,5 @@
+Please note that if you are trying to update **your** website, this is the wrong place to do so. Please carefully follow the [Beautiful Jekyll instructions](https://github.com/daattali/beautiful-jekyll#readme) and make sure you submit changes to **your** version of the project.
+
+If your intention is to submit a Pull Request, please describe what your pull request achieves.
+
+Thank you!