feat(pr-template): add pull request template

.github/pull_request_template.md

@@ -0,0 +1,33 @@
+<!--
+    Thank you for your contribution. Please use this template to help guide
+    you towards preparing a PR that fullfills our merge requirements.
+-->
+# Description
+
+<!-- Describe the changes your PR introduces here. -->
+
+# Issues
+
+<!--
+    Link related issues here, it's ok if this is empty but we do recommend that
+    you create issues before working on PRs, issues on internal trackers are
+    fine and need not be linked here.
+-->
+
+# Checklist
+
+<!--
+    Take care of the default items before marking your PR as ready for review,
+    be prepared to add more items.
+-->
+
+* [ ] This PR contains a description of the changes I'm making
+* [ ] I've read the [Contribution Guidelines](https://github.com/SchweizerischeBundesbahnen/netzgrafik-editor-frontend/blob/main/CONTRIBUTING.md)
+* [ ] I've added tests for changes or features I've introduced
+* [ ] I documented any high-level concepts I'm introducing in `documentation/`
+* [ ] CI is currently green and this is ready for review
+
+<!--
+    Please open PRs as Draft while you make CI green and/or finalise
+    documentation.
+-->