Improve situation around required node version when developing for ACA/ADW.

[binduwavell]

Since both ACA an ADW require an older version of Node, and ideally a specific version range (~14) it would be good to add this information to the documentation and for those of us who make use of the Node Version Manager, if you add a .nvmrc to the root of each of these projects folks can nvm install and nvm use in the project root and get the right version.

The following trick for folks using zsh allows for the nvm to be done automatically: https://github.com/nvm-sh/nvm#zsh