README suggestions

[BigLep]

Some things coming to mind when landing at https://github.com/ipfs/helia-remote-pinning:

1. Rather than have a "Lead Maintainer" section, just codify this in CODEOWNERS? I assume codeowners should be helia-dev.
2. Provide some explanation for why use this package (i.e., it's a convenience wrapper for binding Helia and pinning service providing promise for when certain actions have been completed)
3. The design document is linked in the right hand side project description. Ideally we'd like to design docs from the README.
4. I know covered elsewhere, but link to any relevant examples.
5. Make sure the project is linked from https://github.com/ipfs/helia for discoverability

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