Add a PR template

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,16 @@
+**Replace this text with a summary of the changes in your PR.
+The more detailed you are, the better.**
+
+-----------------
+
+Before submitting the PR make sure the following are checked:
+
+* [ ] The PR relates to *only* one subject with a clear title and description in grammatically correct, complete sentences.
+* [ ] Wrote [good commit messages][1].
+* [ ] Commit message starts with `[Fix #issue-number]` (if the related issue exists).
+* [ ] Feature branch is up-to-date with `master` (if not - rebase it).
+* [ ] Squashed related commits together.
+* [ ] Added tests.
+* [ ] Added an entry to the changelog if the new code introduces user-observable changes. See [changelog entry format](https://github.com/toptal/chewy/blob/master/CONTRIBUTING.md#changelog-entry-format) for details.
+
+[1]: https://chris.beams.io/posts/git-commit/