add documentation for using switch without a control expression

Author: gabehollombe

documentation/coffee/switch_with_no_expression.coffee

@@ -0,0 +1,8 @@
+score = 76
+grade = switch
+  when 90 <= score      then 'A'
+  when 80 <= score < 90 then 'B'
+  when 70 <= score < 80 then 'C'
+  when 60 <= score < 70 then 'D'
+  when       score < 60 then 'F'
+# grade == 'C'

documentation/index.html.erb

@@ -823,6 +823,11 @@ Expressions
     </p>
     <%= code_for('switch') %>
 
+    <p>
+      Switch statements can also be used without a control expression, turning them in to a cleaner alternative to if/else chains.
+    </p>
+    <%= code_for('switch_with_no_expression') %>
+
     <p>
       <span id="try" class="bookmark"></span>
       <b class="header">Try/Catch/Finally</b>