Add spectrum analyser descrtiption.
fix
PPM is selected by either
1) connect MOSI to GND (on the AVRISP connector on OrangeRX receiver)
  - in this mode outputs CH1-CH4 = channel 1-4, CH5 = PPM, CH6-CH8 = channel 5-7
2) connect CH7-CH7 using a jumpper
  - in this mode outputs CH1-CH4 = channel 1-4, CH5 = PPM, CH6 = channel 5

To force binding on RX connect jumpper on CH1-CH2

To make RX act as openLRS spectrum analyser put a jumpper on CH3-CH4, LEDs stay dark in this mode.

It is now possible to disable to "always bind" feature in the openLRSng.ino
Merge branch 'master' of https://github.com/kh4/openLRSng
style fix
README update with new jumpper settings.
Correct the combined mode (AVRISP is shared with CH6-8). 6 channels are available in combined mode as PWM.
Merge branch 'master' of https://github.com/kh4/openLRSng into seriallink