Add examples of GRUB_INIT_TUNE

[積丹尼 Dan Jacobson]

(info "(grub) play")
has no examples of GRUB_INIT_TUNE.
https://askubuntu.com/questions/76309/play-a-sound-before-or-after-grub-loads
has some. Like
GRUB_INIT_TUNE="2000 400 4 0 1 500 4 0 1 600 4 0 1 800 6"
So please add some. Thanks.

Also the paragraph
     If the argument is a file name (*note File name syntax::), play the
     tune recorded in it.  The file format is first the tempo as an
     unsigned 32bit little-endian number, then pairs of unsigned 16bit
     little-endian numbers for pitch and duration pairs.
needs even an example (file) even more.