Add details about the machinery in Inference

[meissnereric]

The class structure is well documented but the details of how it all goes down is less so.

Such topics as:

• apply transformations to variable parameters at the beginning before execution and invert the transform when you ask for it.
• Works by essentially making a whole big gluon block that computes everything - the whole chain
• Where do parameters come from? how do model parameters vs posterior parameters vs gluon block parameters?