Add to the docs what is the unit of measurement for the http_requests_bucket

[royi-frontegg]

responseTime() time param in callback in ms (according to response-time lib docs), and in histogram.observe the value is divided by 1000 So I guess the values are in seconds. I think this should be stated in the docs.

Also I think it might be a good idea to add to the docs a simple prom query & graph to show the values. This is sometimes a huge help for getting up and running quickly