Add note about specifying volume for depletion
Add note about specifying volume for depletion

walshjon/openmc,shikhar413/openmc,amandalund/openmc,amandalund/openmc,walshjon/openmc,shikhar413/openmc,walshjon/openmc,shikhar413/openmc,amandalund/openmc,shikhar413/openmc,walshjon/openmc,amandalund/openmc