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

[Pedro Alves]

On Monday 05 October 2009 20:53:23, Phil Muldoon wrote:

> That reads more clearly than what I wrote. If you don't mind I'll 
> reword, and add the narrative appropriately within the text.

Not at all, and I thank you, even.

-- 
Pedro Alves