Add :npm-deps to the JavaScript Modules guide

[anmonteiro]

One particular caveat to mention is that, in some versions of NPM/Node, users need to have a package.json file present in the directory they're developing in or NPM will install modules to a parent directory.

[swannodette]

Yes please!

[Deraen]

We are also missing a mention that libraries can use :npm-deps in deps.cljs.

[swannodette]

We should circle back and think about what we want to say about JavaScript modules post :target :bundle. While I think we should maintain our JS module support especially ES6 - we should think about how to make this really become an edgecase. I'm warming up to a defclass macro, there's a ticket in JIRA bout this - I think this one are where you have no recourse but to write JS.