add image into demo

index.html

@@ -55,6 +55,7 @@ <h2>Enjoy live editing (+markdown)</h2>
   <hr>
   <p>Horizontal-Rule can be inserted by click「...」on the toolbar or just type「... 」/「--- 」/「*** 」at line start. Note that
     there's a SPACE at the end of a command.</p>
+  <p><img src="https://files.slack.com/files-pri/T02SY1UGK-F02UKR9HH/61fecdffjw1em2euxugtdg208w06okjm.gif" alt="oh my god"/></p>
   <hr>
   <p>To link or unlink, please press the <i>ENTER</i> key after you filled the input field with your a link. A <a
     href="/sofish">link</a> can be unlink by applying an empty value to the input field.