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