Update the seealso entries for namedtuple() (GH-12373)

Update the seealso entries for namedtuple() (GH-12373)

* Replace external recipe link with a link to the dataclasses module.

* Highlight the class definition syntax for typing.NamedTuple
  and add an example for clarity.
(cherry picked from commit 9c68543f022b130ff51944edc6771c60510ee683)

Co-authored-by: Raymond Hettinger <rhettinger@users.noreply.github.com>