webrepl.html: Add hint that 3rd box on the right is for file op status.

Author: Paul Sokolovsky

webrepl.html

@@ -68,7 +68,7 @@
     <input type="button" value="Get from device" onclick="get_file(); return false;" />
   </div>
 
-  <div class="file-box" id="file-status"></div>
+  <div class="file-box" id="file-status"><span style="color:#707070">(file operation status)</span></div>
 
 </div>