Mavericks: rework installation notes

Updated instructions for installing on Mavericks. The key thing is to
make restarting cmd-key-happy use launchctl as this ensures that it is
"cmd-key-happy" that is wanting Accessibility access and not "Terminal".

Addresses issues #11, #12, #13 and #14.

Signed-off-by: Andrew McDermott <andrew.iain.mcdermott@gmail.com>