add missing page description

[bootsa]

There's no clear description of what the website is for from the beginning of the landing page - rather confusing and not very accessible.

The bullet points could relate to a plethora of different types of libraries. I asked ChatGPT - see here.

Seems like there is a description in the source code but the page template doesn't render it on the page (only included in the metadata).

So here's my attempt at adding it.

Please note: I haven't made any attempt at ensuring accessibility, usage in other parts of the site, etc.

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[allejo]

Let me come back to this PR in a bit. I do agree that every page should have a description but I can't say that I agree with the placement of this description, especially for the homepage where that description is in a different spot. I've added a quick bandaid in 02e942a but I do want a better design that touches all the pages