Doc: custom key signature, simplify example

The whole-tone scale conceptually repeats the same pattern
in every octave.

diff --git a/Documentation/snippets/new/non-traditional-key-signatures.ly b/Documentation/snippets/new/non-traditional-key-signatures.ly
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+\version "2.19.7"
+
+\header {
+  lsrtags = "contemporary-notation, pitches, really-cool, staff-notation, version-specific"
+
+  texidoc = "
+The commonly used @code{\\key} command sets the @code{keyAlterations}
+property, in the @code{Staff} context.
+
+To create non-standard key signatures, set this property directly. The
+format of this command is a list:
+
+@code{ \\set Staff.keyAlterations = #`(((octave . step) . alter) ((octave
+. step) . alter) ...) } where, for each element in the list,
+@code{octave} specifies the octave (0 being the octave from middle C to
+the B above), @code{step} specifies the note within the octave (0 means
+C and 6 means B), and @code{alter} is @code{,SHARP ,FLAT ,DOUBLE-SHARP}
+etc. (Note the leading comma.)
+
+
+Alternatively, for each item in the list, using the more concise format
+@code{(step . alter)} specifies that the same alteration should hold in
+all octaves.
+
+
+For microtonal scales where a @qq{sharp} is not 100 cents, @code{alter}
+refers to the alteration as a proportion of a 200-cent whole tone.
+
+
+Here is an example of a possible key signature for generating a
+whole-tone scale:
+
+"
+  doctitle = "Non-traditional key signatures"
+}
+
+
+\relative c' {
+  \set Staff.keyAlterations = #`((6 . ,FLAT)
+                                 (5 . ,FLAT)
+                                 (3 . ,SHARP))
+  c4 d e fis
+  aes4 bes c2
+}