Merge pull request #980 from smoparth/bugfix/issue-968-pr-template

docs: add pull request template with testing checklist

Author: mergify[bot]

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,11 @@
+# Pull Request Description
+
+## What
+
+<!-- Brief description of the change. -->
+
+## Why
+
+<!-- Link to issue (Closes #NNN) or explain the motivation. -->
+
+- [ ] PR follows [CONTRIBUTING.md](https://github.com/python-wheel-build/fromager/blob/main/CONTRIBUTING.md) guidelines