make demo of using this with helia

[Gozala]

I have promised @achingbrain I'll make an example illustrating use of this library with https://github.com/ipfs/helia and then I forgot to do so.

Creating this issue so I actually go and do it.

@achingbrain if there is anything specific you want to be addressed please post here

[alanshaw]

@Gozala @achingbrain here you go:

https://github.com/alanshaw/helia-unixfs-example/blob/6b8e955ddd940190c71e052e0c2be930cf372475/index.js#L1-L41

Where would you like to move it to?

[Gozala]

I would not mind ./examples/helia.js or something in this repo. Maybe something like so we don't have to introduce a dependency

export const demo = (helia) => {
  // ...
}