Describe the job parent which also checks out submodules

Change-Id: Ibbeb90ce1414442fb602c742e0e3d154f135061b
diff --git a/zuul.yaml b/zuul.yaml
index 1f186d0..1bd9f31 100644
--- a/zuul.yaml
+++ b/zuul.yaml
@@ -8,5 +8,7 @@
 
 - job:
     name: run-ci-build-sh-with-submodules
+    description: |
+      Prepare all git submodules and continue as `run-ci-build-sh`.
     parent: run-ci-build-sh
     pre-run: playbooks/git-submodules/run.yaml