[Documentation request] Document, what `txdelay` and `rxdelay` actually do and what the mechanics behind is.

[dreirund]

From confusion on what txdelay and rxdelay really do and what the mechanics behind is, I hereby have a documentation request to have this thoroughly documented, and a link to that documentation added to the repeater CLI documentation.

For now, it seems that it is only hidden in code, so one has to be able to read and understand the source code to get to know what those settings actually mean and do.

Regards!