Backport from 3.2: improve argument/parameter documentation (issue #15990).

The corresponding 3.x commits are 69d5d834c5cb, 40fd26a4206b, and
74d8a2a20c52.
diff --git a/Misc/NEWS b/Misc/NEWS
index a7d2da6..89f7e22 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -594,6 +594,8 @@
 Documentation
 -------------
 
+- Issue #15990: Improve argument/parameter documentation.
+
 - Issue #16400: Update the description of which versions of a given package
   PyPI displays.