Doc - add description of scope for interface intro page

Author: samaaron

etc/doc/tutorial/01.2-Exploring-the-Interface.md

@@ -15,7 +15,7 @@ little time exploring it.
 * *E* - Prefs Panel
 * *F* - Log Viewer
 * *G* - Help System
-
+* *H* - Scope Viewer
 
 ## A. Play Controls
 
@@ -70,10 +70,22 @@ is doing.
 
 ## G. Help System
 
-Finally, one of the most important parts of the Sonic Pi interface is
+One of the most important parts of the Sonic Pi interface is
 the help system which appears at the bottom of the window. This can be
 toggled on and off by clicking on the blue *Help* button. The help
 system contains help and information about all aspects of Sonic Pi
 including this tutorial, a list of available synths, samples, examples,
 FX and a full list of all the functions Sonic Pi provides for coding
 music.
+
+## H. Scope Viewer
+
+The scope viewer allows you to see the sound you're hearing. You can
+easily see that the saw wave looks like a saw and that the basic beep is
+a curvey sine wave. You can also see the difference between loud and
+quiet sounds by the size of the lines. There are 3 scopes to play with -
+the default is a combined scope for the left and right channels, there
+is a stereo scope which draws a separate scope for each channel. Finally
+there is a Lissajous curve scope which will show the phase relationship
+between the left and right channels and allows you to draw pretty
+pictures with sound (https://en.wikipedia.org/wiki/Lissajous_curve).