Document `Shipping` mode

[jecaro]

Shipping mode doesn't use as much battery as Deep sleep mode. It is super useful, hence it should be documented.

See also pimoroni/badger2350#8

[jakobi]

@pimoroni: please document this somewhere easy to find :)

I had the same issue and found nothing in threads nor documentation, nor in the tufty repo:

how to store them without having them turn on.

Reset/Boot is easy to solve, and are required to resume or boot: glue a rubber piece below to protect against accidental presses.

To also disable the frontbuttons, I found that I could put the sleep by pressing any other button before long pressing sleep (incl. the home/boot button).

I found the code (cf. powman; but its just 2 locations, plus the factory test code) in question in the search below, which confirmed my observation.

https://github.com/search?q=repo%3Apimoroni%2Ftufty2350%20shipping%20mode&type=code