Doc: NR improve 1.6.3 examples (issue 5448129)

[dak]

http://codereview.appspot.com/5448129/diff/1/Documentation/notation/staff.itely
File Documentation/notation/staff.itely (right):

http://codereview.appspot.com/5448129/diff/1/Documentation/notation/staff.itely#newcode869
Documentation/notation/staff.itely:869: }
As explained previously, _this_ _will_ _not_ _work_.  You need to
enclose the music following \with { ... } in braces or only the very
first term will belong to the new Staff.

http://codereview.appspot.com/5448129/diff/1/Documentation/notation/staff.itely#newcode886
Documentation/notation/staff.itely:886: }
Again, the following music needs to be enclosed in braces so that it is
actually part of the Staff.  Later examples are changed appropriately,
so this is likely just an oversight.

http://codereview.appspot.com/5448129/