Multi-Strip Support Doc for ESP32 should note "Input Only" pins

[Peeeet]

The WLED UI does helpfully warn you if you try to use "input only" pins on the ESP32 for the strip outputs, but this info does not show up anywhere in WLED documentation - though I did find this forum thread after already soldering stuff and then wondering why I couldn't use pins 34 and 35.

I'm sure it's common ESP32 developer knowledge that pins 34 through 39 are input only, but one could understand the confusion for a newbie like myself considering they're all still called "GPIO" in all the pinouts - which of course stands for "general purpose input and output"...

[blazoncek]

Hi. You are welcome to update the documentation. Just fork, make changes and submit a PR.