Improve understanding of Category filters by adding link to the Category Help page

We should have the d.o team create a redirect url like drupal.org/category-help and we should link to that; that way if the page URL ever changes or the node ID does or something, the link won't break.

1) work with DA/d.o webmasters to create redirect
2) determine UI for adding the help / link
3) add into svelte code near the categories filter

(I don't think this will need a test)

I'm working on this issue as part of DrupalCon Portland.

I updated the css and removed the svg from the repo.

Rebased. I don't have any design reference to know what this should look like, so I'm just posting what it looks like at the current point.

I think this needs some work:

• Link to drupal.org → should be to a permalink rather than an alias, so /node/3421718
• Link needs an alt text.
• Ideally this would be a popup? But to be consistent with say About text formats on editing pages, it should open in a new window?

Along with the feedback from #10,

• I think the question mark (?) should also display some short text in a tooltip
• We could also consider having tooltip text for each category so that on hover it could be easily read rather than everytime reading on the Help page.