Mention the git-change script in the README

Signed-off-by: Gustavo L. de M. Chaves <gnustavo@cpan.org>
Fix indentation

Signed-off-by: Gustavo L. de M. Chaves <gnustavo@cpan.org>
Consolidate Gerrit configuration in the git-gerrit.remote variable

Previously we needed to set up several variables in the git-gerrit
section (protocol, username, hostname, and port). It's easier to
simply require the user to setup a HTTP remote for her Gerrit server
and infer what we need from there.

Signed-off-by: Gustavo L. de M. Chaves <gnustavo@cpan.org>