fix decode error and write some doc

SuperScriptViewer/templates/viewer.html

@@ -25,7 +25,7 @@
 
         </div>
         <div style="width: 100px;">
-            <button style="width: 100px; height: 50px;">LEGEND</button>
+            <button style="width: 100px; height: 50px;">Help</button>
         </div>
     </div>
     <div style="background: #7f7f7f; width: 100%; height: 100%; overflow: scroll; position: relative;">