[docs] fix and improve current docs

[ASKabalan]

Creating this issue to write a todo list for fixing the docs in furax

• wrong name in furax title

  furax/docs/source/conf.py

  Line 14 in e9ad33f

  project = 'jax-healpy'

• remove comp_sep optional dependencies from docs and toml
• Add more basic examples
• Add incremental learning docs (Stokes => Operators => combining operators => creating custom operator
• Make sure there is an example for each user facing API

Feel free to add more

[sbiquard]

• furax/docs/source/index.rst

  Line 63 in e9ad33f

  weighted_data = weight_op @ stokes_data

  (should be weight_op(stokes_data) right?). I think the same thing happens in other places.

Edit: #62 fixed most of these already

[sbiquard]

Reopening since #75 didn't address all of the items in the original post