Improve k8 discovery docs.
Improve k8 discovery docs.

Fix formatting.
Remove long example from reference documentation, point off
to existing example instead.

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