[methods] Add a short intro to usability methodology

[dbosk]

Different students design security systems on different levels --- e.g. sysadmins chooses and configures software, can influence policies etc. --- as such, they need some insights into how best to get good usability results. For the engineering students it's more obvious why they need it, and hopefully they have a full course on usability methodology, but a reminder would be good for them anyway.

[dbosk]

From #3: Perhaps some material from chid can be useful here too. Or at least used as a base.

[dbosk]

Jakob Nielsen: First Rule of Usability? Don't Listen to Users

They also have a lot more useful material here.