Added docstrings to model methods
Added docstrings to model methods

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