doc/README

context: work around `long` not existing on Python 3

I can't figure out what this branch is even trying to accomplish, and
it was introduced in ac89a23ca814 which doesn't really shed any
insight into why longs are treated differently from ints.

Mercurial's documentation is kept in reStructuredText format, which is
a simple plain text format that's easy to read and edit:

  http://docutils.sourceforge.net/rst.html

It's also convertible to a variety of other formats including standard
UNIX man page format and HTML. You'll need to install Docutils:

  http://docutils.sourceforge.net/

Use the Makefile in this directory to generate the man and HTML pages.