[PATCH 3 of 3] histedit: add extension docstring from external README

[Matt Mackall]

On Fri, 2012-07-06 at 12:20 -0500, Augie Fackler wrote:
> # HG changeset patch
> # User Augie Fackler <raf at durin42.com>
> # Date 1341595073 18000
> # Node ID d7ade18c7f240910682cbe5347a27a895370b2f0
> # Parent  b82996a9a48a5beddf0b7ae101e8d2911b55561c
> histedit: add extension docstring from external README

These are queued for default, thanks.

-- 
Mathematics is the supreme nostalgia of our time.