Mention proxy_url in the docs.
Mention proxy_url in the docs.

tcolgate/docs,tcolgate/docs,ddfreyne/prometheus-docs,ddfreyne/prometheus-docs,open-falcon/open-falcon.github.io,du2016/prometheus-docs,chosenken/docs,open-falcon/open-falcon.github.io,prometheus/docs,Cepave/openfalcon.io,du2016/prometheus-docs,open-falcon/open-falcon.github.io,du2016/prometheus-docs,prometheus/docs,chosenken/docs,Cepave/openfalcon.io,chosenken/docs,ddfreyne/prometheus-docs,ddfreyne/prometheus-docs,prometheus/docs,chosenken/docs,tcolgate/docs,Cepave/openfalcon.io