Updated input docs with surface label descriptor
Updated input docs with surface label descriptor

smharper/openmc,liangjg/openmc,walshjon/openmc,johnnyliu27/openmc,amandalund/openmc,kellyrowland/openmc,lilulu/openmc,shikhar413/openmc,wbinventor/openmc,liangjg/openmc,mit-crpg/openmc,samuelshaner/openmc,mit-crpg/openmc,walshjon/openmc,walshjon/openmc,smharper/openmc,smharper/openmc,liangjg/openmc,kellyrowland/openmc,bhermanmit/openmc,bhermanmit/openmc,shikhar413/openmc,amandalund/openmc,shikhar413/openmc,amandalund/openmc,shikhar413/openmc,wbinventor/openmc,amandalund/openmc,mjlong/openmc,samuelshaner/openmc,liangjg/openmc,mjlong/openmc,lilulu/openmc,johnnyliu27/openmc,paulromano/openmc,wbinventor/openmc,paulromano/openmc,walshjon/openmc,johnnyliu27/openmc,johnnyliu27/openmc,paulromano/openmc,wbinventor/openmc,paulromano/openmc,samuelshaner/openmc,lilulu/openmc,mit-crpg/openmc,samuelshaner/openmc,mit-crpg/openmc,smharper/openmc