title: How to use and add icon to a cell in ag-grid to indicate the cell is editable
body: <p>I am using ag-grid with angular 6. For a particular column the cell is supposed to be editable. Please find the below image.</p>
  
  <p><a href="https://i.stack.imgur.com/oZO1X.png" rel="noreferrer"><img src="https://i.stack.imgur.com/oZO1X.png" alt="enter image description here"></a></p>
  
  <p>How can i add this icon, on click of which the cell is made editable. </p>