tests/README

hgrc.5: drop 'hgext.' prefix when talking about extensions

The first paragraph apply to all extensions, not just those in hgext.
The second paragraph can just use the simpler form to load mq.

To run the tests, do:

cd tests/
python run-tests.py

See http://mercurial.selenic.com/wiki/WritingTests for
more information on writing tests.