[tz] Fix example for zic transition coalescence

I noticed a typo in zic.8 within the "correct" example given for how zic handles/coalesces certain transitions. While I was there, it also made sense to expand a bit more on where the incorrect interpretation could come from, as a further nod to why we choose instead to have zic coalesce transitions as it does. Documentation patch attached and pushed to the development repository. -- Tim Parenti