Add usage documentation

[Ellipse0934]

Instead of linking to the blog post we should have basic usage instructions here itself. Because:

1. There is a discrepancy in the docker image url. Post suggests freshtracks.io/avalanche meanwhile the README gives prometheuscommunity/avalanche. I assume we want to suggest the latter.
2. The blogpost has images which cannot be copy pasted for convenience and must be manually written.
3. Editorial control should be maintained in the repo .

I'm happy to make a PR on this. I think we should suggest a compose file:

version: "3.0"
services:
  prometheus:
    container_name: prometheus
    image: prom/prometheus
    ports:
      - "9090:9090"
    volumes:
      - ./config/Prometheus.yml:/etc/prometheus/prometheus.yml
    networks:
      - prom
  avalanche:
    container_name: avalanche
    image: quay.io/prometheuscommunity/avalanche:main
    ports:
      - "9001:9001"
    networks:
      prom:
        aliases:
          - avalanche
networks:
  prom:
    name: prom

[Ellipse0934]

I have a tree with this work but I'm not happy with it. https://github.com/Ellipse0934/avalanche/tree/ap/readme

I think I'll wait until there are a few more features merged in and someone available to review.

[bwplotka]

Where do we link blog post? Perhaps we fixed it already? I will assume it's done and close it, we can reopen later. (: