Add pull request template

Inspired by u-boot, this tells developers who come across our repository
on Github to use Gerrit instead of submitting pull requests.

Signed-off-by: Joel Stanley <joel@jms.id.au>
Change-Id: I57dfa346416d306075b530f318dd58134e6b39fa
diff --git a/.github/pull_request_template.md b/.github/pull_request_template.md
new file mode 100644
index 0000000..55a1b0a
--- /dev/null
+++ b/.github/pull_request_template.md
@@ -0,0 +1,3 @@
+Please do not submit a Pull Request via github.  Our project makes use of
+Gerrit for patch submission and review.  For more details please
+see https://github.com/openbmc/docs/blob/master/CONTRIBUTING.md#submitting-changes-via-gerrit-server