fix documentation

[federicobriata]

https://github.com/geekworm-com/x728/blob/e630e268238490a1632a517b9af3ce817a088044/x728-v2.0.sh#L75

Hi Guys, plz add to your documentation references on all x728 PINS and not just on Raspberry Pi's GPIO. I.e. from v2 the PIN33 (GPIO13) is replaced by the PIN37 (GPIO26), atm wiki doc jumps from x728 v1.3 to v2.1 and this code is the only place to find the gpio but still no information on PIN37.

A part this, x728 it's really good stuff!!!

FYI I had problem with RPi.GPIO python library on NON Raspberry PI SBC with Raspberry Pi compatibility PINs (I'm testing Odroid C2), so I decided to replace all python stuff with bash equivalent and merge everything in a single pwr script started from a systemd service file included in this script. TODO: Buzzer is still not implemented yet. Then I don't have a Raspberry Pi to more test and Odroid C2 device become on production. Hope to see in your python more support on web monitor side too. Have fun! https://github.com/federicobriata/x728-script/