Update installation guide to include submodules

Author: agarwalrounak

docs/install.rst

@@ -77,7 +77,7 @@ you need these libraries.
 Get and run Read the Docs
 -------------------------
 
-Clone the repository somewhere on your disk, initialize and update the submodule, and enter to the repository::
+Clone the repository somewhere on your disk and enter to the repository::
 
     git clone --recurse-submodules https://github.com/rtfd/readthedocs.org.git
     cd readthedocs.org