Clarify docs: PublicDirectory.read returns a CID (for now)

[matheus23]

Right now these are the docs for the wasm PublicDirectory.read function:

rs-wnfs/wnfs-wasm/src/fs/public/directory.rs

Lines 115 to 116 in 0726da2

	/// Reads specified file content from the directory.
	pub fn read(&self, path_segments: &Array, store: BlockStore) -> JsResult<Promise> {

It should perhaps be clarified that only a CID is returned.

In the future we'll have rs-wnfs code that understands UnixFS chunking and will be able to stream out the actual bytes of the file.

[matheus23]

This was addressed in #376