Finish the design docs

[bbatsov]

I've noticed that the sections on font-locking and indentation are missing in https://github.com/clojure-emacs/clojure-ts-mode/blob/main/doc/design.md#syntax-highlighting

@rrudakov Would be interested in tacking this given all the recent work you've done on both fronts? I think it'd be great to have as much documentation on the subject as possible to make it easier for more people to contribute in the future.

[rrudakov]

Sure, I've missed this document completely :) Will check it out.

[bbatsov]

Thanks!