Make textare readonly.

backend/src/Squidex/wwwroot/scripts/editor-log.html

@@ -22,11 +22,12 @@
         <button id="button">Generate New Value</button>
     </div>
 
-    <textarea id="textarea"></textarea>
+    <textarea readonly id="textarea"></textarea>
 
     <script>
         var numberGenerator = 1;
 
+        // The button to generate a new value.
         var button = document.getElementById('button');
 
         var textarea = document.getElementById('textarea');