add documentation

[rroohhh]

Add documentation about the firmware image

• basic login, accessing the camera over serial or ssh
• basic scripts and camera tools
• installing software and updating the image / software
• wifi / ethernet connection
• how to add your own software

Do we also need documentation for basic linux tasks like creating a user or the basic unix commands (cd, ls, rm, etc.)?
I think we should rely on external documentation for the basic linux stuff.

While writing this documentation the manual should be updated aswell.

[rroohhh]

possible choice for the documentation of linux basics:

• http://wiki.lib.sun.ac.za/images/c/ca/TLCL-13.07.pdf
• http://linuxcommand.org/lc3_learning_the_shell.php

[se6astian-pi]

Started documentation for this specific firmware 2.0 for testers:
https://wiki.apertus.org/index.php/AXIOM_Beta_Firmware_Version_2.0