Add NEWS entries for the ImportWarning change and documentation update

Misc/NEWS

@@ -25,6 +25,8 @@ Core and builtins
 Library
 -------
 
+- warnings.py now ignores ImportWarning by default
+
 - Patch #1517790: It is now possible to use custom objects in the ctypes
   foreign function argtypes sequence as long as they provide a from_param
   method, no longer is it required that the object is a ctypes type.
@@ -115,6 +117,9 @@ Tests
 Documentation
 -------------
 
+- Cover ImportWarning, PendingDeprecationWarning and simplefilter() in the
+  documentation for the warnings module.
+
 - Patch #1509163: MS Toolkit Compiler no longer available.