README: Improve description of precompiled bytecode; mention mpy-cross.
README: Improve description of precompiled bytecode; mention mpy-cross.

deshipu/micropython,dmazzella/micropython,pfalcon/micropython,MrSurly/micropython-esp32,ryannathans/micropython,Timmenem/micropython,pozetroninc/micropython,TDAbboud/micropython,tralamazza/micropython,torwag/micropython,MrSurly/micropython,kerneltask/micropython,infinnovation/micropython,henriknelson/micropython,torwag/micropython,HenrikSolver/micropython,deshipu/micropython,pramasoul/micropython,henriknelson/micropython,tobbad/micropython,pfalcon/micropython,trezor/micropython,adafruit/circuitpython,dmazzella/micropython,oopy/micropython,PappaPeppar/micropython,bvernoux/micropython,SHA2017-badge/micropython-esp32,MrSurly/micropython-esp32,AriZuu/micropython,selste/micropython,oopy/micropython,swegener/micropython,oopy/micropython,adafruit/circuitpython,blazewicz/micropython,lowRISC/micropython,bvernoux/micropython,chrisdearman/micropython,alex-robbins/micropython,selste/micropython,PappaPeppar/micropython,pramasoul/micropython,chrisdearman/micropython,adafruit/micropython,oopy/micropython,PappaPeppar/micropython,MrSurly/micropython-esp32,adafruit/circuitpython,micropython/micropython-esp32,pozetroninc/micropython,SHA2017-badge/micropython-esp32,adafruit/micropython,trezor/micropython,AriZuu/micropython,pozetroninc/micropython,ryannathans/micropython,pfalcon/micropython,micropython/micropython-esp32,MrSurly/micropython,pozetroninc/micropython,HenrikSolver/micropython,adafruit/micropython,HenrikSolver/micropython,tobbad/micropython,HenrikSolver/micropython,Timmenem/micropython,PappaPeppar/micropython,pramasoul/micropython,alex-robbins/micropython,infinnovation/micropython,kerneltask/micropython,TDAbboud/micropython,trezor/micropython,PappaPeppar/micropython,infinnovation/micropython,AriZuu/micropython,deshipu/micropython,alex-robbins/micropython,bvernoux/micropython,alex-robbins/micropython,chrisdearman/micropython,lowRISC/micropython,selste/micropython,adafruit/circuitpython,swegener/micropython,trezor/micropython,dmazzella/micropython,adafruit/micropython,dmazzella/micropython,Timmenem/micropython,oopy/micropython,bvernoux/micropython,alex-robbins/micropython,kerneltask/micropython,tobbad/micropython,tobbad/micropython,MrSurly/micropython,lowRISC/micropython,henriknelson/micropython,swegener/micropython,chrisdearman/micropython,blazewicz/micropython,SHA2017-badge/micropython-esp32,tralamazza/micropython,henriknelson/micropython,infinnovation/micropython,AriZuu/micropython,trezor/micropython,MrSurly/micropython-esp32,AriZuu/micropython,torwag/micropython,infinnovation/micropython,tobbad/micropython,micropython/micropython-esp32,Timmenem/micropython,ryannathans/micropython,selste/micropython,kerneltask/micropython,lowRISC/micropython,selste/micropython,MrSurly/micropython-esp32,pramasoul/micropython,blazewicz/micropython,lowRISC/micropython,tralamazza/micropython,TDAbboud/micropython,Timmenem/micropython,TDAbboud/micropython,pozetroninc/micropython,blazewicz/micropython,adafruit/circuitpython,chrisdearman/micropython,micropython/micropython-esp32,pfalcon/micropython,torwag/micropython,MrSurly/micropython,tralamazza/micropython,adafruit/micropython,TDAbboud/micropython,adafruit/circuitpython,bvernoux/micropython,torwag/micropython,micropython/micropython-esp32,pramasoul/micropython,swegener/micropython,deshipu/micropython,MrSurly/micropython,kerneltask/micropython,pfalcon/micropython,SHA2017-badge/micropython-esp32,blazewicz/micropython,ryannathans/micropython,ryannathans/micropython,deshipu/micropython,swegener/micropython,HenrikSolver/micropython,SHA2017-badge/micropython-esp32,henriknelson/micropython