added note regarding loading custom archetypes

git-svn-id: svn://svn.openvpms.org/openvpms/release/branches/1.8-dev@6219 9e4fa352-aafb-0310-9071-df624684024b
Added migration for OBF-232 Change serialisation of IMObjectReference for details nodes to enable comparison

git-svn-id: svn://svn.openvpms.org/openvpms/release/branches/1.8-dev@6227 9e4fa352-aafb-0310-9071-df624684024b