Added description of ACE Law 66 in documentation.
Added description of ACE Law 66 in documentation.

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