README: frop --recurse-submodules flag

Author: chalin

README.md

@@ -56,7 +56,7 @@ theme changes), making sure you have installed all the prerequisites listed
 above:
 
 ```console
-$ git clone --recurse-submodules --depth 1 https://github.com/google/docsy.git
+$ git clone --depth 1 https://github.com/google/docsy.git
 $ cd docsy/userguide/
 $ npm install
 $ npm run serve