Add 'bug report' button

InvenTree/templates/about.html

@@ -28,6 +28,10 @@
                         <tr>
                             <td>View Code on GitHub</td><td><a href="{% inventree_github %}">{% inventree_github %}</a></td>
                         </tr>
+                        <tr>
+                            <td></td>
+                            <td><a href='https://github.com/inventree/InvenTree/issues'><button class='btn btn-default'>Submit Bug Report</button></a></td>
+                        </tr>
                     </table>
 
                 </div>