Add a mention to setup.py.

Author: abergeron

doc/installation.rst

@@ -133,7 +133,7 @@ MacPorts, but this is untested and unsupported.
 
 It appears that on some versions, /usr/local is not in the default
 compiler paths so you might need to add ``-L /usr/local/lib -I
-/usr/local/include`` to the command line to build the python module.
+/usr/local/include`` to the ``setup.py build`` command.
 
 
 Windows-specific instructions