Update test_deprecate_nonkeyword_arguments.py

Update documentation string.

Author: alexitkes

pandas/tests/util/test_deprecate_nonkeyword_arguments.py

@@ -71,8 +71,8 @@ def test_four_arguments():
 @deprecate_nonkeyword_arguments(version="1.1")
 def g(a, b=0, c=0, d=0):
     """
-    Sum of one to four numbers, the two last arguments
-    should be given as keyword arguments only
+    Sum of one to four numbers, but three of them have default
+    values, so may be given as keyword arguments only.
     """
     return a + b + c + d