Suggestion: sv add docs link to project page of official add-ons

[rmunn]

Having a list of addons in https://svelte.dev/docs/cli/sv-add is very useful. It could be even more useful if each available addon had a one-line description, or at least a link to the addon's official project page. For some addons it's pretty obvious what they do, but for others a link or a description would be very helpful. For example, unless you already know what mdsvex is, you're unlikely to know that that's what you want to be able to use Markdown in your Svelte components.

[manuel3108]

Agree, duplicates #241