Add to arduino settings, to additional bards manager URLs

http://drazzy.com/package_drazzy.com_index.json

adds the https://github.com/SpenceKonde/ATTinyCore library with support for ATtiny chips, including the ATtiny841.

copy paste the contents of the attiny841.conf to avrdude.conf file to add the support for the chip for AVRdude for programming it.

WireS-Master is the library for arduino to use the ATtiny841 as a slave in I2C network, the compatibility is so complete you can use the existing slave code for the normal Wire library, just by changing the name of the library.