Added new PR template (#5598)

* Copied PR template from bazel-contrib/rules_go#2425
* Merge branch 'master' into new-pr-template
* Merge refs/heads/master into new-pr-template
* Merge refs/heads/master into new-pr-template
* Merge refs/heads/master into new-pr-template
* Merge refs/heads/master into new-pr-template

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,30 @@
+<!-- Thanks for sending a PR! Before submitting:
+
+1. If this is your first PR, please read CONTRIBUTING.md and sign the CLA
+   first. We cannot review code without a signed CLA.
+2. Please file an issue *first*. All features and most bug fixes should have
+   an associated issue with a design discussed and decided upon. Small bug
+   fixes and documentation improvements don't need issues.
+3. New features and bug fixes must have tests. Documentation may need to
+   be updated. If you're unsure what to update, send the PR, and we'll discuss
+   in review.
+4. Note that PRs updating dependencies and new Go versions are not accepted.
+   Please file an issue instead.
+-->
+
+**What type of PR is this?**
+
+> Uncomment one line below and remove others.
+>
+> Bug fix
+> Feature
+> Documentation
+> Other
+
+**What does this PR do? Why is it needed?**
+
+**Which issues(s) does this PR fix?**
+
+Fixes #
+
+**Other notes for review**