Add GitHub PR template
This template directs contributors to submit the contribution to the
Gerrit instance, which is the source of truth (GitHub is just a mirror).
Change-Id: I4f234c96e269d3ba054b6d3905ceff0291990e68
diff --git a/.github/pull_request_template.md b/.github/pull_request_template.md
new file mode 100644
index 0000000..fc66768
--- /dev/null
+++ b/.github/pull_request_template.md
@@ -0,0 +1,15 @@
+<!--
+ ⚠️ IMPORTANT
+
+ Hi there! Thanks for contributing!
+
+ This project uses Gerrit for code review. Please, submit your pull
+ request there so we can review it:
+ * https://gerrit.avm99963.com/
+
+ You can learn how to do that in the following document:
+ * https://gerrit.avm99963.com/Documentation/intro-gerrit-walkthrough-github.html
+
+ If you're not comfortable using Gerrit, you can submit your pull
+ request here at GitHub and we'll manually transfer it to Gerrit :)
+-->