Add script to extract from xml files

[BurnySc2]

XML files can be found in
https://github.com/Ahli/sc2xml
https://github.com/SC2Mapster/SC2GameData

For the script to work, the file structure needs to be

extract/collect_balance_data.py
extract/mods/*.sc2mod/...

XML files can be extracted from SC2 using stormex CLI tool
https://github.com/Talv/stormex

Command to extract XML files:

 ./stormex path_to_sc2_installation/Program Files (x86)/StarCraft II/ -s .xml -x -o ./out

For more info, check the updated README.md file