Improve documentation
Improve documentation

(refs #9638)

YaqiWang/moose,YaqiWang/moose,bwspenc/moose,jessecarterMOOSE/moose,permcody/moose,lindsayad/moose,nuclear-wizard/moose,harterj/moose,SudiptaBiswas/moose,SudiptaBiswas/moose,sapitts/moose,lindsayad/moose,jessecarterMOOSE/moose,milljm/moose,laagesen/moose,bwspenc/moose,nuclear-wizard/moose,sapitts/moose,dschwen/moose,lindsayad/moose,sapitts/moose,andrsd/moose,bwspenc/moose,idaholab/moose,idaholab/moose,laagesen/moose,bwspenc/moose,harterj/moose,milljm/moose,YaqiWang/moose,andrsd/moose,SudiptaBiswas/moose,permcody/moose,milljm/moose,harterj/moose,SudiptaBiswas/moose,laagesen/moose,jessecarterMOOSE/moose,milljm/moose,sapitts/moose,bwspenc/moose,dschwen/moose,milljm/moose,lindsayad/moose,laagesen/moose,dschwen/moose,idaholab/moose,jessecarterMOOSE/moose,laagesen/moose,idaholab/moose,andrsd/moose,andrsd/moose,permcody/moose,lindsayad/moose,harterj/moose,dschwen/moose,nuclear-wizard/moose,idaholab/moose,YaqiWang/moose,andrsd/moose,permcody/moose,harterj/moose,SudiptaBiswas/moose,nuclear-wizard/moose,dschwen/moose,sapitts/moose,jessecarterMOOSE/moose