Pull Request template for goog.module PRs

Provide a standard pull request template more suited to PRs doing
goog.module conversions.

There's no way to pick a non-default template when creating a PR
manually, but this one can be used by adding
"&?template=goog_module.md" to the
https://github.com/cpcallen/bugs/compare/ URL.

.github/PULL_REQUEST_TEMPLATE/goog_module.md

@@ -0,0 +1,20 @@
+<!-- Suggested PR title: Migrate path/to/file.js to goog.module syntax -->
+
+## The basics
+
+- [ ] I branched from `goog.module`
+- [ ] My pull request is against `goog.module`
+- [ ] My code follows the [style guide](
+      https://developers.google.com/blockly/guides/modify/web/style-guide)
+- [ ] My code is presented in the form suggeseted in the [module
+      conversion guide](https://github.com/google/blockly/issues/5026)
+- [ ] I have run `npm test` locally already.
+
+## The details
+### Resolves
+
+Part of #5026
+
+### Additional Information
+
+<!-- Anything else we should know? -->