Document self-hosting options

Needs

At least mention in README that points people in the right direction
- could be article on docs.ipfs.io, or a link to docker image etc
is there any open source implementation for a self-hosted, AWS S3-backed ipfs pinning service that conforms to the Pinning service API? or backed by any high-scale centralized storage

Options to investigate:

https://ipfscluster.io
- we already provide docker images etc
- supports a subset of the pinning service api since v1.0.0 (https://github.com/ipfs/ipfs-cluster/issues/1213)
- needs docs how to use it for self-hosted service, how to set up Authorization: Bearer <access-token> etc
https://github.com/ipfs-elastic-provider/ipfs-elastic-provider is probably not ready yet
- does not support pinning service api on its own
- providing on DHT requires running hydra boosters

If anyone has time to comment on their experiences, or even document self-hosting setup end-to-end, that will be very useful.