[Doc]: Improve style and navigation of documentation site

[tomvothecoder]

Describe your documentation update

• The documentation homepage for xarray and uxarray is simple and straightforward. It uses tables and navigation links to other pages.

  • https://docs.xarray.dev/en/stable/index.html
  • https://uxarray.readthedocs.io/en/latest/

• The gallery homepage includes tables to each of the notebooks:

  • https://docs.xarray.dev/en/stable/gallery.html
  • https://uxarray.readthedocs.io/en/latest/examples.html

• The contributors page should also be updated to be more stylish:

  • https://xarray.dev/team