Document how to create your own build with custom inflators

[vincentfretin]

I made the package to be reusable (I defined exports in packages.json) so you can do your own build with customized gltfInflators.
More or less import the components you want, and the inflators you want, and register them like in
https://github.com/c-frame/aframe-gltf-model-plus/blob/main/src/inflators/index.js