[libstdc++] Add brief documentation narrative for GDB pretty-printers. Add links to GDB wiki/manual

[Tom Tromey]

>>>>> "Benjamin" == Benjamin Kosnik <bkoz@redhat.com> writes:

Benjamin> If you want WAA for libstdc++ (given your CL entries for the
Benjamin> python work it might be a good idea) please fill out the webform. I'm
Benjamin> willing to approve.

Phil, I set you up.
Please send and commit a patch for the gcc MAINTAINERS file.

thanks,
Tom