Implement Concept Widget

[angelikatyborska]

In about.md of one JavaScript concept I tried to use a concept widget as described in https://exercism.lol/docs/building/markdown/widgets

 [concept:<track-slug>/<concept-slug>]()

It's on the last line of this file: https://raw.githubusercontent.com/exercism/javascript/main/concepts/array-destructuring/about.md

[concept:javascript/rest-and-spread]()

It doesn't render as promised in the docs. It renders as broken link (no href) attribute.

[iHiD]

@ErikSchierboom If you get chance to do this, I think you know the code better and it might be quick for you (I can style it if you can render it), but prioritise F#/C#/Ruby first if it'll take you more than 15mins, and I'll find time to implement it before launch.

[iHiD]

Concept widgets now render as links (so stuff doesn't look broken). We'll render the actual widgets post-launch.