Mention using Git submodule for adding themes.

content/pelican.rst

 Blogging with Pelican
-########################
+#####################
 :date: 2014-04-19
 :summary: How I blog with Pelican
 
@@ -85,11 +85,12 @@ I've set the timezone to mine (so that the time of published articles is correct
 
 Themes
 ------
-Pelican comes with a default theme (the same as used by Pelican's website) but I wanted something more understated so I took at look at `https://github.com/getpelican/pelican-themes <https://github.com/getpelican/pelican-themes>`_ and chose pelican-mockingbird. Cloned it
+Pelican comes with a default theme (the same as used by Pelican's website) but I wanted something more understated so I took at look at `https://github.com/getpelican/pelican-themes <https://github.com/getpelican/pelican-themes>`_ and chose pelican-mockingbird. Either clone it or add it as a git submodule (depends on if you're using Git to version control your blog or not)
 
 .. code:: shell
 
-    git clone https://github.com/wrl/pelican-mockingbird.git
+    git clone https://github.com/wrl/pelican-mockingbird.git #If you're not using Git.
+    git submodule add https://github.com/wrl/pelican-mockingbird.git #If you're using Git.
 
 and set the theme to that by adding the following to pelicanconf.py: ::