Doc: NR 1.5.2: Clarify voice order; \shiftOn etc. (issue2226045)

[tdanielsmusic]

I'm not particularly opposed to placing this in the
NR, but it's not clear what you are suggesting here.
Do you mean to leave the LM unchanged, or do you intend
to remove or change the corresponding section there?


Also, if it is to go in the NR it needs a separate
section heading.  At the moment it appears under
"The double backslash construct", whereas it applies
equally to explicitly instantiated voices.  Maybe
something like "Voice order"?


http://codereview.appspot.com/2226045/