Merge pull request #2903 from owenniblock/docs/add-notes-on-rest

add a section on how to use :r

Author: samaaron

etc/doc/tutorial/02.1-Your-First-Beeps.md

@@ -122,4 +122,7 @@ play :E4
 If you want to make a note sharp, add an `s` after the note name such as
 `play :Fs3` and if you want to make a note flat, add a `b` such as `play :Eb3`.
 
+There's also a handy shortcut for a rest (a musical way of saying not to play 
+anything instead of a note) using `:r`, `:rest` or `nil`.
+
 Now go *wild* and have fun making your own tunes.