[Docs] argument for disabling collectors not documented

[ToMe25]

As far as I can tell, there is no documentation for --no-collector.NAME disabling a collector anywhere.

Last time I checked I couldn't even find this documentation for the node exporter, and had to help articles on stackoverflow to figure this out.

But even if the node exporter documents this somewhere it would be nice if either this exporter, or this GitHub repository would document this behavior somewhere.

[ToMe25]

After thinking about it again, and looking at some other software I think using a help line like this --[no-]collector.cpu Enable the cpu collector (default: enabled). would be a good option, though I have no idea about how to do that with kingpin.

[lukasmalkmus]

Feel free to tackle this. I'll keep the issues open. But at the moment I don't have capacity to work in this exporter apart from occasional maintenance.

[ToMe25]

I opened these recent issues mostly to track these things, I don't consider them to have any significant urgency.

I will look into implementing some of them if and when I find the time and motivation to do so :)