doc: moduel doc for weakref.pyx

kivy/weakproxy.pyx

@@ -1,6 +1,17 @@
+"""
+Weak Proxy
+==========
+
+In order to allow garbage collection, the weak proxy provides
+`weak references <https://en.wikipedia.org/wiki/Weak_reference>`_ to objects.
+It effectively enhances the
+`weakref.proxy <https://docs.python.org/2/library/weakref.html#weakref.proxy>`_
+by adding comparison support.
+"""
 import weakref
 import operator
 
+
 cdef class WeakProxy(object):
     '''Replacement for weakref.proxy to support comparisons
     '''