Add PR template (#925)

.github/PULL_REQUEST_TEMPLATE/default.md

@@ -0,0 +1,10 @@
+<!--
+Thank you for contributing to Writers' Toolkit!
+
+Consider the following checklist to make sure your PR is most effective.
+-->
+
+- [ ] I've used a relevant pull request (PR) title.
+- [ ] I've added a link to any relevant issues in the PR description.
+- [ ] I've checked my changes on the deploy preview and they look good.
+- [ ] I've added an entry to the [What's new](https://github.com/grafana/writers-toolkit/blob/main/docs/sources/whats-new.md) page (only required for notable changes).