bpo-42360: Add advice to help avoid pickling issues. (GH-23305) (GH-23429)

diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index 549ac1b..2ffdb49 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -849,6 +849,9 @@
     Named tuple instances do not have per-instance dictionaries, so they are
     lightweight and require no more memory than regular tuples.
 
+    To support pickling, the named tuple class should be assigned to a variable
+    that matches *typename*.
+
     .. versionchanged:: 3.1
        Added support for *rename*.