docs/library/index: Add important summary of the intro section as warning.
docs/library/index: Add important summary of the intro section as warning.

To make them harder to miss.

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