Add a way/instructions on how to use with figwheel-main instead of shadow-cljs

[stathissideris]

No description provided.

[kiranshila]

So, I think the story is that the :npm-deps in deps.cljs work fine, as in cljs knows to grab the node deps, but it still needs the externs. The :require statements in the various places I use the node modules are Shadow specific, so I'm not quite sure how to make them do nothing for non-shadow builds.

The other half of the story is none of remark + plugins I need are on CLJSJS, so we would need to manually go in there and generate all of those externs.

[kiranshila]

Now that our cljs requires are using the modern $default syntax, this should be able to work with cljsjs dependencies.