Fix usage of include labels in group modifiers.
Fix usage of include labels in group modifiers.

The final change to the group modifiers requires included labels
to be on the "many"-side of the operation. This adjusts the example
and description to match this behavior.

bluecmd/prometheus-docs,ddfreyne/prometheus-docs,tcolgate/docs,vic3lord/docs,du2016/prometheus-docs,pdbogen/docs,open-falcon/open-falcon.github.io,ddfreyne/prometheus-docs,dln/docs,du2016/prometheus-docs,dato/prometheus-docs,tcolgate/docs,Cepave/openfalcon.io,open-falcon/open-falcon.github.io,Cepave/openfalcon.io,prometheus/docs,evanphx/docs,ChaoticMind/docs,ddfreyne/prometheus-docs,chosenken/docs,du2016/prometheus-docs,ddfreyne/prometheus-docs,dato/prometheus-docs,jmptrader/docs,vic3lord/docs,Cepave/openfalcon.io,jimmidyson/docs,evanphx/docs,jmptrader/docs,chosenken/docs,chosenken/docs,jimmidyson/docs,fabxc/docs,open-falcon/open-falcon.github.io,pdbogen/docs,prometheus/docs,fabxc/docs,tcolgate/docs,dato/prometheus-docs,jmptrader/docs,dln/docs,vic3lord/docs,prometheus/docs,pdbogen/docs,ChaoticMind/docs,jimmidyson/docs,chosenken/docs,dln/docs,bluecmd/prometheus-docs,ChaoticMind/docs,evanphx/docs,bluecmd/prometheus-docs,fabxc/docs