add dd flashing to docs

[x70b1]

Is your feature request related to a problem? Please describe.

balenaEtcher is great. It is very colorful and simply designed.

But it is an overhead. Also, I have to run it as root otherwise I can't write to my SD card. I don't want to use GUI tools as root. An easy and popular solution would be dd. Something like this works fine:

dd if=pwnagotchi-raspbian-lite-v1.2.1.img of=/dev/mmcblk0 bs=4M

Describe the solution you'd like

A hint in the docs abou dd would be nice.

[evilsocket]

I've took for granted that if instead of using balenaEtcher you want to use dd, it's because you know already how to do it :D but yeah, fair

[x70b1]

Sounds good. But I wasn't sure if balenaEtcher do something magical.