Redesign the front page of the docs

[leouieda]

Remove the wall of text and make clear boxes for getting started, asking for help, API reference, and citing. Include the full table of contents underneath to help with navigation. Move the text about different use cases to a "Why Pooch?" page. Introduces the sphinx-panels extension to use cards, columns, and tabs.

Preview of the built docs: https://www.leouieda.com/docs-previews/pooch/238/

Reminders:

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst and the base __init__.py file for the package.
• Write detailed docstrings for all functions/classes/methods. It often helps to design better code if you write the docstrings first.
• If adding new functionality, add an example to the docstring, gallery, and/or tutorials.
• Add your full name, affiliation, and ORCID (optional) to the AUTHORS.md file (if you haven't already) in case you'd like to be listed as an author on the Zenodo archive of the next release.

[leouieda]

@prisae @aguspesce @santisoler what do you think?

[prisae]

I like it, I think it makes it easier to get started. Also the new tabs on the About and Installing sections look neat!

[santisoler]

This looks awesome! I ❤️ the tabs! And the cards in the front page looks amazing.

The only thing I would change is the color of the text inside the buttons when hovering. Currently, when hovering over the buttons, the text inside them is shown in the same original blue color, while the button itself fills with another tone of blue, drastically lowering the contrast of the text and its background. Besides the aesthetics, I think we should change that to improve accessibility.

[leouieda]

Thanks @santisoler @prisae! That was an easy fix. Merging this in!