Update README

[Jeansen]

Installation without Kubernetes only shows a pull command, but nothing more. There should be some more input, e.g. on how to run the proxy. Also, helm needs https but providing the relevant environment variable results in an error (only shown un shutdown of the container) because ocip expects certs/registry.pem and certs/registry-key.pem.

Since I have harbor running on the same host, it was quite easy to get it running (for me), e.g.:

docker run --rm --name helm-charts-oci-proxy -p 9000:9000 -e USE_TLS=true -v /data/cert/proxy-ng.cert:/certs/registry.pem:ro -v /data/cert/proxy-ng.key:/certs/registry-key.pem:ro 8gears.container-registry.com/library/helm-charts-oci-proxy

With this setup, I was able to do an example helm pull.

I thought about a PR, but then decided it would be better if the original authors would amend/update the README. While they are on it, I bet there will be more points to cover or review.

On the other hand, if I can help with a simple PR, I'd gladly update the README! :-)

[Vad1mo]

Hello,
Makes to better outline use cases outside k8s or alongside harbor.

Happy accept improvements

V

[Jeansen]

OK, I'll create a PR then, soon.