Add codeviewKeepButton to plugin document.

Author: Diemen Design

03-plugins.md

@@ -188,6 +188,10 @@ The vars below are not all needed, what you need depends on what your trying acc
 
           // tooltip for button
           tooltip: lang.examplePlugin.tooltip,
+
+          // Stop button from being disabled when in CodeView
+          codeviewKeepButton: true,
+
           click:function (e) {
             context.invoke('examplePlugin.show');
           }