Small documentation fixes

missing packages & qt version <=5.13

Why is glew included in the list? WE should not require it anymore as its included now. Is it a dependency of the others?

I had a compile error with a missing include. It seems we accidentally rely on system glew somewhere.

I'll try to reproduce it to figure out where that was.

Great, just want to get rid of the external dependency

mentioned in commit 5cc32d37

merged