Core: Add User Manual

[mbahler]

Discussed in #124

^{Originally posted by bonner72 January 14, 2026}
@mbahler what do you think about creating a user manual? I suppose it's not really necessary, being the software is incredibly simple, but it could come in handy for the absolute beginner. I would suggest just a small pdf document.

It could possibly be linked to display via command as well?

[mbahler]

Possibly create either a web-viewer to view a wiki page, or a builtin PDF viewer.