Doc: Added @knownissue to Grace Notes for MIDI (issue4388041)

[Carl . D . Sorensen]

Looks generally good, but I think we need to include the error message
text in the @knownissue.

Thanks,

Carl



http://codereview.appspot.com/4388041/diff/1/Documentation/notation/rhythms.itely
File Documentation/notation/rhythms.itely (right):

http://codereview.appspot.com/4388041/diff/1/Documentation/notation/rhythms.itely#newcode3241
Documentation/notation/rhythms.itely:3241:
I think the known issue should include the warning; something like "If
the total length of the grace notes is greater than the duration of the
preceding note, the error message "Going back in MIDI time" will be
generated. "  That will give the user the clue about their particular
music, I think.

http://codereview.appspot.com/4388041/