Add instructions to the wiki for turning off the ACT LED on RPi Zero

[per1234]

Unlike the other RPi boards, the Raspberry Pi Zero's ACT LED is active low so following the instructions at https://github.com/ccrisan/motioneyeos/wiki/Turn-Off-LEDs causes the ACT LED on the RPi Zero to be permanently on. I suggest adding the following text to that page:

For Raspberry Pi Zero:

# Disable the ACT LED.
dtparam=act_led_trigger=none
dtparam=act_led_activelow=on

While I'm on the subject of that page I'd also like to suggest that if #184 is going to be mentioned there should be a link to that issue, which can be accomplished with the following markdown:

As mentioned in [Issue #184](https://github.com/ccrisan/motioneyeos/issues/184).

renders as:
As mentioned in Issue #184.

[bortek]

thanks for suggestion. Wiki page updated.

[Jachimo]

Perhaps worth noting that I don't think the suggestions in the Wiki work on ThingOS currently? I don't think it has a /boot/config.txt that is easily editable. The same thing can be accomplished (if you don't mind the lights flashing momentarily on boot) by putting a couple of lines into /data/etc/userinit.sh instead. Perhaps not as thorough a solution...

[jasaw]

@Jachimo boot partition is mounted read-only by default. To remount it as read-write, run this command mount -o remount,rw,noatime,sync /boot and you should be able to edit /boot/config.txt.

[desegura]

for pi zero 2 w run: echo 0 | tee /sys/class/leds/led0/brightness