Update documentation for the folding preferences

Add the information about the new (experimental) folding feature
introduced by eclipse-jdt/eclipse.jdt.ui#1562

Author: fedejeanne

eclipse.platform.common/bundles/org.eclipse.jdt.doc.user/reference/preferences/java/editor/ref-preferences-folding.htm

@@ -91,6 +91,17 @@ <h1>Java Editor Folding Preferences</h1>
 			<p>On</p>
 			</td>
 		</tr>
+		<tr>
+			<td valign="top">
+			<p>Extended folding (experimental) \ Activate feature</p>
+			</td>
+			<td valign="top">
+			<p>If enabled, folding will be active for several other kinds of code blocks like loops, if statements, etc.</p>
+			</td>
+			<td valign="top">
+			<p>Off</p>
+			</td>
+		</tr>
 	</tbody>
 </table>
 <h3 class="related">Related References</h3>