Document the changelog about ppx log syntax.
Document the changelog about ppx log syntax.

ocsigen/lwt,rneswold/lwt,c-cube/lwt,rgrinberg/lwt,rneswold/lwt,rneswold/lwt,ocsigen/lwt,rgrinberg/lwt,c-cube/lwt,c-cube/lwt,mfp/lwt,mfp/lwt,ocsigen/lwt,rgrinberg/lwt,rgrinberg/lwt