Explain Bucklescript's name mangling rule

Bucklescript has name mangling rules (as explained in [`genType`'s documentation](https://github.com/cristianoc/genType/tree/91e6c498bee5b77ef4743c104fa474f8d7bf07b8#renaming-gentypeas-and-object-mangling-convention)) which are not explained at all in the official documentation. Can we add them? I can make a PR if the maintainers can tell me where to add them.	