Changed a word in docs to clarify meaning
Changed a word in docs to clarify meaning

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