Document additional features in espixelboard

[penfold42]

This fork includes support for many things that espixelstick can’t or won’t support.
Already done but not documented:

• PWM support on gpios including inverted logic and digital output for relays
• Gpio twiddling via http get and websocket
• Rotary encoder support for manual on device control of RGB and HSV
• 16 bit gamma tables (only useful for pwm)
• UDP raw packet protocol (with stats on main page and config - enable, port number)
• Config backup and restore
• old style MQTT (as well as the newer json based MQTT)
• reworked admin page
• effectengine can send led data to other sticks

DONE and merged upstream:

• live updates to gamma changes
• Auto enable effect after n seconds of no data
• Separated stream view in web UI

TODO

• basic source IP based ACLs
• integrate rotary encoder and effect engine
• oled display support ?
• GPIO reading in WebUI and PWM config