clarified docstrings
clarified docstrings

walshjon/openmc,mit-crpg/openmc,liangjg/openmc,wbinventor/openmc,liangjg/openmc,amandalund/openmc,smharper/openmc,johnnyliu27/openmc,mit-crpg/openmc,johnnyliu27/openmc,paulromano/openmc,liangjg/openmc,smharper/openmc,bhermanmit/openmc,paulromano/openmc,wbinventor/openmc,johnnyliu27/openmc,liangjg/openmc,amandalund/openmc,smharper/openmc,walshjon/openmc,paulromano/openmc,amandalund/openmc,shikhar413/openmc,shikhar413/openmc,mit-crpg/openmc,walshjon/openmc,mit-crpg/openmc,johnnyliu27/openmc,amandalund/openmc,shikhar413/openmc,shikhar413/openmc,bhermanmit/openmc,wbinventor/openmc,paulromano/openmc,smharper/openmc,walshjon/openmc,wbinventor/openmc