docs: Update intro page

[caksoylar]

Attempt to update the intro page to docs, converting the comparison table to a feature/capabilities list. Then, split it into categories and add new items for in-progress work.

The last two are split into different commits, if you want to see intermediate states (but I'll squash them all into one before merging).

[caksoylar]

Question: Is it better to use subheadings rather than table header rows for category names?

[Nick-Munnich]

Agree that this has been overdue. Aside from my minor comments, my biggest complaint is how the tables appear on the page. If it's possible to center the legend table and move the keymap and connectivity tables to be on the right of the hardware table when there is the space for it, that'd improve the situation massively for me. Other alignment stuff too.

[caksoylar]

Aside from my minor comments, my biggest complaint is how the tables appear on the page.

I agree with this, it doesn't look good. I don't know if we can easily put tables side-by-side. My initial thought was making the tables full width like https://zmk.dev/docs/keymaps/list-of-keycodes, which seems to require using a custom element rather than a markdown table, to add a bit of CSS. Or we can go back to a single table.

[caksoylar]

I gave the two column suggestion @Nick-Munnich had a shot, using the implementation from https://docusaurus.community/knowledge/component-library/new/Columns/. It still isn't perfect but seems better, I am open to other ideas.

[Nick-Munnich]

I think it looks good, I'm happy.

[petejohanson]

LGTM! Thanks!