Add steps for shadow-cljs build

[nickdex]

Hey, this tool looks awesome. I'm new to clojure world (and build options are the most complex things in it 😅 ). Can you please add steps to integrate it with shadow-cljs (without add code modifications).

[knubie]

There is an example shadow-cljs project here: https://github.com/binaryage/cljs-devtools/tree/master/examples/shadow