Clarify the behavior of the staticmethod builtin (GH-4362)

Objects/funcobject.c

@@ -838,7 +838,8 @@ PyClassMethod_New(PyObject *callable)
              ...
 
    It can be called either on the class (e.g. C.f()) or on an instance
-   (e.g. C().f()); the instance is ignored except for its class.
+   (e.g. C().f()). Both the class and the instance are ignored, and
+   neither is passed implicitly as the first argument to the method.
 
    Static methods in Python are similar to those found in Java or C++.
    For a more advanced concept, see class methods above.
@@ -945,7 +946,8 @@ To declare a static method, use this idiom:\n\
              ...\n\
 \n\
 It can be called either on the class (e.g. C.f()) or on an instance\n\
-(e.g. C().f()).  The instance is ignored except for its class.\n\
+(e.g. C().f()). Both the class and the instance are ignored, and\n\
+neither is passed implicitly as the first argument to the method.\n\
 \n\
 Static methods in Python are similar to those found in Java or C++.\n\
 For a more advanced concept, see the classmethod builtin.");