Update index.html

I have always found your service to be very convenient. However, I have noticed that sometimes when I paste text, it can be difficult to read. Therefore, I would like to suggest that you consider implementing a spellcheck function.

index.html

@@ -225,7 +225,7 @@ <h2>Options</h2>
   </div>
 
   <div class="editor">
-    <textarea id="source"></textarea>
+    <textarea id="source" spellcheck="false"></textarea>
   </div>
 
   <div class="hide">