Add info how to compile javascript

[tobiasKaminsky]

I think some info on how to compile things are needed

• inform which node and npm version is needed (e.g. by looking into package.json)
• how to get node
  • install nvm
  • install node via nvm: e.g. nvm install 14.17.0
• how to install npm
  • e.g. npm i -g npm@7.20.6

I think this would help inexperienced devs and lowers entry barrier.

This would is meant as a starting point, to help people, not having a clear c&p instructions (which would change probably too often).