Add HACKING.md
Add HACKING.md

jhegedus42/try-reflex,ryantrinkle/try-reflex,paldepind/try-reflex,ajnsit/reflex-platform,reflex-frp/reflex-platform,meiersi/try-blaze-react,ocharles/try-reflex,reflex-frp/reflex-platform,reflex-frp/reflex-platform,unisonweb/unison-dependencies