Change link to Gerrit tutorial in PR template

The new tutorial targets GitHub users and it is much shorter than the
other one.

Change-Id: I3c5deb43b0fc756658373e33669ab1b091427a13
diff --git a/.github/pull_request_template.md b/.github/pull_request_template.md
index 4daf3fd..fc66768 100644
--- a/.github/pull_request_template.md
+++ b/.github/pull_request_template.md
@@ -8,7 +8,7 @@
   * https://gerrit.avm99963.com/
 
   You can learn how to do that in the following document:
-  * https://gerrit.avm99963.com/Documentation/intro-gerrit-walkthrough.html
+  * 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 :)