Bug in page:Advanced APIs

Section "Advanced File System API" have no explanation for every method.

I working on implementing my own file system, and i can't understand what to do, because documentation do not have API description.

For example i've checked [MEMFS implementation](https://github.com/emscripten-core/emscripten/blob/main/src/library_memfs.js#L241) and i want to understand what a `FS.createNode` call do, i go to https://emscripten.org/docs/api_reference/advanced-apis.html#FS.createNode but there are no any elaboration what this method do.

URL: [../../docs/api_reference/advanced-apis](https://emscripten.org/docs/api_reference/Filesystem-API.html#filesystem-api)


# Proposal

Explain what every method do and optionally add short description how to implement own file system and examples if possible