title: onOpen not executing?
body: <p>Hi guys im trying to display a sidebar on my google sheets every time it is opened. I am using the onOpen function and calling the html page, but it is not executing. When i run the function manually it works, however it doesnt execute on its own when the google sheet is opened. 
  Here is my code: </p>
  
  <pre><code>.gs code: 
  
  function onOpen(){
         var html = HtmlService.createHtmlOutputFromFile('tipA')
        .setWidth(300);
         SpreadsheetApp.getUi() // Or DocumentApp or FormApp.
        .showSidebar(html); 
  }
  
  .html code: 
  
  &lt;!DOCTYPE html&gt;
  &lt;html&gt;
    &lt;head&gt;
    &lt;/head&gt;
    &lt;body&gt;
     &lt;div&gt;
     &lt;p&gt; Some text &lt;p&gt; 
     &lt;p&gt;&lt;img src="some link" alt="xyz" width=240 height=210&gt;&lt;/p&gt;
     &lt;/div&gt;
    &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>