Added section on rotating angles in documentation.
Added section on rotating angles in documentation.

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