chore: add PR template (#650)

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,10 @@
+##### Description of Change
+<!-- Describe your PR here, in enough detail that a reviewer can understand its purpose easily. -->
+
+##### Checklist
+<!-- Remove items that do not apply. For completed items, change [ ] to [x]. -->
+
+- [ ] PR description included and stakeholders cc'd
+- [ ] Patch information is added to appropriate `.patches.yaml`
+- [ ] `script/update` runs without error
+- [ ] PR title follows semantic [commit guidelines](https://github.com/electron/electron/blob/master/docs/development/pull-requests.md#commit-message-guidelines)