Making the new-style d-portal docs live

[robredpath]

The new-style d-portal docs are well underway; I'm quite keen to get them into use as soon as we can, even as we continue to work on them. In particular, I'm keen to move as much content as we can off the website and into the d-portal docs as part of simplifying the website content.

I'd like to understand what else remains in order to get to the point that the new d-portal docs are the d-portal docs.

I think this includes:

• Updating the design system so that it's clear how you get back to a tool from its docs site
• Setting up DNS and ReadTheDocs for docs.d-portal.org
• Changing links on d-portal itself - e.g. the FAQ link on the homepage
• After we're done, removing unused pages from the d-portal codebase for cleanliness

Anything else to start with, @IsabelBirds ?