Added description of ACE Law 1 in documentation.
Added description of ACE Law 1 in documentation.

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