added OTP information

[Niklap97]

• updated Nitrokey App 2 feature list
• added Passwords entry for Windows and Linux

[daringer]

Should we maybe organize the items below "Nitrokey App 2" like this:

• Installing Windows
• Installing Linux
• Passwords

Personally I don't see how putting "Passwords" below "Windows" respectively "Linux" will add value. What do you think?

[Niklap97]

@daringer this can be merged now, right?