README: Update command for cloning gerrit to include --recurse-submodules

Change-Id: I6539500d20b20a4c67e23fae16519703dfadd024

README.md

diff --git a/README.md b/README.md
index 575d450..65b95b4 100644
--- a/README.md
+++ b/README.md
@@ -90,7 +90,7 @@
 
 ```
   git clone https://gerrit.googlesource.com/plugins/owners
-  git clone https://gerrit.googlesource.com/gerrit
+  git clone --recurse-submodules https://gerrit.googlesource.com/gerrit
   cd gerrit/plugins
   ln -s ../../owners/owners .
   ln -s ../../owners/owners-autoassign .