doc: fix indentation in usage into the Python console

BoboTiG · BoboTiG · commit 420dafb09593 · 2016-10-04T18:44:40.000+02:00
diff --git a/docs/source/usage.rst b/docs/source/usage.rst
@@ -74,6 +74,8 @@ A screenshot to grab them all::
 Into the Python's console
 -------------------------
 
+.. code:: python
+
     >>> from mss import mss
     >>> sct = mss(display=b':0')
 
