Adding idiotproof instructions for apt-based linux systems

Never had to install this package before, so it may be worth a mention.
Trying out JAX one line at a time...

Stumbled upon it by chance. It really should be the top result of [this search](https://www.google.com/search?hl=en&q=tested+webgl+library). (incidentally, this is the search I made before defaulting to three.js, and you can bet I was not the only one)

JAX is a [tested webgl library](http://blog.jaxgl.com/what-is-jax) and should be recognized as such by big G. (see what I did there ?)