changed url format for better prometheus integration

[kbudde]

Hi,

I had to no idea how to integrate your nice little script into prometheus. I've changed the endpoint and added an example config for prometheus. This works for me.
Perhaps you have a better idea?

BR

Kris

[brian-brazil]

prometheus/prometheus#861 is the other part of this, as that'll handle escaping too

[brian-brazil]

That's upstream now, and the readme explains how to use it so this change isn't needed.