added altclick select to selectfeatures example

examples/select-features.html

@@ -3,7 +3,7 @@ template: example.html
 title: Select features example
 shortdesc: Example of using the Select interaction.
 docs: >
-  Choose between <code>Single-click</code>, <code>Click</code> and <code>Hover</code> as the event type for selection in the combobox below. When using <code>Single-click</code> or <code>Click</code> you can hold do <code>Shift</code> key to toggle the feature in the selection.</p>
+  Choose between <code>Single-click</code>, <code>Click</code>, <code>Hover</code> and <code>Alt+Click</code> as the event type for selection in the combobox below. When using <code>Single-click</code> or <code>Click</code> you can hold do <code>Shift</code> key to toggle the feature in the selection.</p>
           <p>Note: when <code>Single-click</code> is used double-clicks won't select features. This in contrast to <code>Click</code>, where a double-click will both select the feature and zoom the map (because of the <code>DoubleClickZoom</code> interaction). Note that <code>Single-click</code> is less responsive than <code>Click</code> because of the delay it uses to detect double-clicks.</p>
   <p>In this example, a listener is registered for the Select interaction's <code>select</code> event in order to update the selection status below.
   <form class="form-inline">
@@ -13,6 +13,7 @@ docs: >
         <option value="singleclick">Single-click</option>
         <option value="click">Click</option>
         <option value="pointermove">Hover</option>
+        <option value="altclick">Alt+Click</option>
       </select>
       <span id="status">&nbsp;0 selected features</span>
   </form>