Update index to reflect change to available examples

Author: diarmidmackenzie

examples/index.html

@@ -88,19 +88,9 @@ <h3>Examples</h3>
             <td>❌</td>
           </tr>
           <tr>
-            <td><a href="platforms/">Platforms</a></td>
-            <td>physics, locomotion</td>
-            <td>❌</td>
-          </tr>
-          <tr>
-            <td><a href="playground/">Playground</a></td>
-            <td>physics</td>
-            <td>❌</td>
-          </tr>
-          <tr>
-            <td><a href="walls/">Walls</a></td>
-            <td>physics, locomotion</td>
-            <td>❌</td>
+            <td><a href="tubes/">Tubes</a></td>
+            <td>a-tube</td>
+            <td>✅</td>
           </tr>
         </tbody>
       </table>