Mention we only support linux based os for vuestic-ui development on 20th node

[asvae]

• Probably somewhere in docs for contributors we have to mention that if they use windows - they should also use wsl to avoid trouble (it might work on windows, but we don't test it).

• Same for node

[asvae]

Probably something like "To start developing vuestic-ui you should first set up your environment".

• We should also ensure we have nvmrc and node version in engines. (maybe not? is it truly necessary?)