update README (#106)
update README (#106)

- make doc more understandable
- add `-d` for `docker run` to support run in the backgroud

Signed-off-by: Xiang Dai <f274b132786a051b69171fb6599acffc1400c4a5@qq.com>
grafana/loki,grafana/loki,grafana/loki,grafana/loki,grafana/loki,grafana/loki