doc/README

hgweb: allow viewing diffs against p1 or p2 for merge commits (issue3904)

This adds UI portion of the feature that has resided in mercurial since 2012.
Back then the interface was added together with the code, but was shortly
backed out because it was deemed "not ready". Code, however, stayed.

For the original feature and its implementation, see issue2810 and
d605a82cf189.

In short, the backed-out interface had two outstanding issues:
1. it was introducing an entirely new term (baseline) and
2. it was present on every changeset's page, even for changesets with 1 parent
   (or no parents), which didn't make sense

This patch implements a hopefully better interface because:
1. it uses the usual terms (diff) and
2. it only shows up when there actually are 2 parents.

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.