Documentation: Hotkeys: hulk mode not documented

[martin-henz]

Currently, hulk mode is not documented:

I think it's a useful feature for everyone to know about, so it should be included in the table:
"make the background of the major frontend components green (00FF00) for use with tools that have a green screen option"

[RichDom2185]

The shortcut will need to be changed following #2968

[chownces]

The shortcut will need to be changed following #2968

After #2968 is merged, the new hotkey will be alt+shift+h. See #2968 for more details regarding the change.