[REVIEW] docs for developer + main pages of ModelArray & ConFixel

[zhao-cy]

quickly go thru:

• [x] docs for developer
  • [x] most important is the section model fitting
• [x] main page of ModelArray
• [x] main page of ConFixel

The latest version has been merged into main, and has been deployed i.e., can be directly viewed with the links above

[TinasheMTapera]

Done, no major comments