Clarify how namepaths work for modules

[hegemonic]

The docs use namepaths like module:color/mixer when discussing CommonJS/Node.js modules. In jsdoc/jsdoc#863, it was pointed out that this could be confusing, because color/mixer isn't a valid npm module name. In this case, module:color/mixer would refer to the file mixer/index.js within the color module.

We should try to clarify this issue in the docs.