Add documentation for undervoltage lockout and amphour/watthour features.

[Ralim]

What kind of documentation do you think would be appropriate? Happy to look at having a go at adding some stuff to the wiki?

[Arachnid]

Thanks for the offer! The commands need documenting here. We probably should port that over to a wiki page, though.

[Ralim]

@Arachnid Is there anything else that should be added?

[Arachnid]

To the documentation? A quick guide to building the firmware yourself wouldn't hurt. :)