Added description of method of successive generations.
Added description of method of successive generations.

paulromano/openmc,keadyk/openmc_mg_prepush,amandalund/openmc,sxds/opemmc,kellyrowland/openmc,amandalund/openmc,sxds/opemmc,walshjon/openmc,paulromano/openmc,shikhar413/openmc,mjlong/openmc,shikhar413/openmc,smharper/openmc,johnnyliu27/openmc,paulromano/openmc,bhermanmit/cdash,walshjon/openmc,lilulu/openmc,bhermanmit/openmc,lilulu/openmc,shenqicang/openmc,mit-crpg/openmc,samuelshaner/openmc,smharper/openmc,liangjg/openmc,walshjon/openmc,johnnyliu27/openmc,keadyk/openmc_mg_prepush,wbinventor/openmc,mjlong/openmc,smharper/openmc,mit-crpg/openmc,smharper/openmc,samuelshaner/openmc,mit-crpg/openmc,samuelshaner/openmc,johnnyliu27/openmc,nhorelik/openmc,wbinventor/openmc,liangjg/openmc,shikhar413/openmc,shenqicang/openmc,walshjon/openmc,amandalund/openmc,wbinventor/openmc,amandalund/openmc,liangjg/openmc,johnnyliu27/openmc,samuelshaner/openmc,paulromano/openmc,wbinventor/openmc,nhorelik/openmc,liangjg/openmc,shikhar413/openmc,bhermanmit/openmc,kellyrowland/openmc,lilulu/openmc,mit-crpg/openmc,keadyk/openmc_mg_prepush