Add controller box dissamebly guide and code protect info

[JulLeuverink]

Since it is the hardest part of the whole installation it would be nice to have a reference to a dissasembly guide for the controller box in the installation walkthrough.

I have found two excellent ones:

• https://www.youtube.com/watch?v=jCPlM2KYwDQ
• https://www.ifixit.com/Teardown/Ikea+Bekant+Controller+Teardown/142516

It seems like Ikea has put some effort into securing the controller box due to projects like this and the megadesk project.
It is hard to proof but what I have seen online and my dissasembly of the box leads me to the conclusion that they use more ultrasonic welding spots to secure the backplate to the box. Furthermore they protect their code for the microcontroller (#5).
Would be nice to have a hint in the documentation that the code in newer versions of the table may be protected.
We know that they protect the code at least since 2019.
A dump has been uploaded in #2. As of now nobody has reported on a roll back on this dump to a controller that had protected code.