Updated user manual for 0.3 (todo: screenshots)

Updated the description, @ageis will take care of the screenshots.
You should add something here to the effect of: "The best way to protect your codename is to memorize it. If you cannot memorize it right away, we recommend writing it down and keeping it in a safe place at first, and gradually working to memorize it over time. Once you have memorized it, you should destroy the written copy."