doc that popover content() is given the element as an arg; fix #13175

docs/_includes/js/popovers.html

@@ -193,7 +193,10 @@ $('.popover-dismiss').popover({
           <td>content</td>
           <td>string | function</td>
           <td>''</td>
-          <td>Default content value if <code>data-content</code> attribute isn't present</td>
+          <td>
+            <p>Default content value if <code>data-content</code> attribute isn't present.</p>
+            <p>If a function is given, it will be called with 1 argument, which is the element that the popover is attached to.</p>
+          </td>
         </tr>
         <tr>
           <td>delay</td>