Hm, I believe this is not actually necessary.
At least it seems to work for me in the rescript-lang.org repo. I just changed something in the loader:
rescript-lang.org/app/routes/BlogRoute.res at master · rescript-lang/rescript-lang.org · GitHub
and it updated immediately in the browser.
So it seems you just need a .resi file for it to work?
Bear in mind we use .jsx everywhere in the docs repo, not sure if that makes a difference.