Added the pull request template

Author: agronholm

.github/pull_request_template.md

@@ -0,0 +1,30 @@
+<!-- Thank you for your contribution! -->
+## Changes
+
+Fixes #. <!-- Provide issue number if exists -->
+
+<!-- Please give a short brief about these changes. -->
+
+## Checklist
+
+If this is a user-facing code change, like a bugfix or a new feature, please ensure that
+you've fulfilled the following conditions (where applicable):
+
+- [ ] You've added tests (in `tests/`) which would fail without your patch
+- [ ] You've added a new changelog entry (in `CHANGES.rst`).
+
+If this is a trivial change, like a typo fix or a code reformatting, then you can ignore
+these instructions.
+
+### Updating the changelog
+
+If there are no entries after the last release, use `**UNRELEASED**` as the version.
+If, say, your patch fixes issue <span>#</span>123, the entry should look like this:
+
+```
+- Fix big bad boo-boo in task groups
+  (`#123 <https://github.com/agronholm/sqlacodegen/issues/123>`_; PR by @yourgithubaccount)
+```
+
+If there's no issue linked, just link to your pull request instead by updating the
+changelog after you've created the PR.