add --recursive in contributing guide (python-telegram-bot#664)

Eldinnie · jh0ker · commit 25912dca6e0f · 2017-06-14T00:02:16.000+02:00
diff --git a/.github/CONTRIBUTING.rst b/.github/CONTRIBUTING.rst
@@ -12,7 +12,7 @@ Setting things up
 
    .. code-block:: bash
 
-      $ git clone https://github.com/<your username>/python-telegram-bot
+      $ git clone https://github.com/<your username>/python-telegram-bot --recursive
       $ cd python-telegram-bot
 
 3. Add a track to the original repository:
