[tz] leap second theory

I was trying to point someone to a reference describing how the "right" zones can be used to enable a system to handle leap seconds more correctly, but I discovered that this isn't really documented anywhere. (There's Steve Allen's page at https://www.ucolick.org/~sla/leapsecs/right+gps.html , of course, but that describes a distinct variant of the scheme.) Would it make sense to add something like the attached patch to theory.html?