Add README to the js build to explain how to build.

[phckr]

Feature Description

I can generate a buttplug.min.js with yarn build:publish -- this is good.

However, I don't know how to generate the 1.buttplug.min.js and the wasm module.

Maybe it is obvious, in which case I would appreciate a quick note telling me where to look.

[wolfsprite]

Same issue. Also could not get it working even when downloading the 1.buttplug.min.js and various .map files and referencing locally. :(