fix docs

docs/usage.rst

@@ -5,19 +5,32 @@ To use snakehouse just use the following in your :code:`setup.py`:
 
 .. code-block:: python
 
-    list_of_pyx_files = [ ... ]
+    from snakehouse import Multibuild, build
+
+    extensions = build([
+                    Multibuild('example_module', list_of_pyx_files)
+                    ], compiler_directives={
+                       'language_level': '3',
+                    })
 
     setup(name='example_module',
       version='0.1',
       packages=['example_module'],
-      ext_modules=Multibuild('example_module', list_of_pyx_files)
+      ext_modules=extensions
     )
 
-Full documentation of Multibuild is here
+You can pass also :code:`setuptools`'s :code:`Extensions` objects, as detailed in
+example_.
+
+.. _example: https://github.com/smok-serwis/snakehouse/blob/develop/example/setup.py
+
+Full pydoc of :code:`Multibuild` and :code:`build` is here
 
 .. autoclass:: snakehouse.Multibuild
     :members:
 
+.. autofunction:: snakehouse.build
+
 You should use :code:`dont_snakehouse` for debugging and unit tests, as
 snakehouse has a sad tendency to dump core on unhandled exceptions. To prevent that
 from happening remember to handle your exceptions and debug using this flag.