Add FAQ about TLS and authentication.
Add FAQ about TLS and authentication.

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