Move learning network stuff into new category?

[ablaom]

After revisiting this site after a long time, I find it disturbing that the learning network stuff (everything after and including "Composing Models") lives in the "Getting Started" section, as it is way too advanced and likely putting new users off.

Perhaps we need an Advanced section.

Thoughts?

cc @EssamWisam

[EssamWisam]

Indeed, I find it overwhelming for new users. Expect a PR that adds a new "Advanced" category to the navigation bar somewhat soon.

[EssamWisam]

Closed thanks to #210