Document dependency on sane devel (#24)

Author: manisandro

README.rst

@@ -14,7 +14,7 @@ maintained by Ralph Heinkel. It is currently maintained by Sandro Mani.
 Build
 -----
 
-To build this module, type::
+To build this module, make sure the sane development package is installed. Then, type::
 
 	python setup.py build