Add an anchor directly to the boot menu animation

wiki/src/install/inc/steps/pc_boot_menu.inline.html

@@ -92,7 +92,7 @@ following screenshot is an example of a boot menu:</p>
 
 </ol>
 
-<p>This animation explains how to use the boot menu key:</p>
+<p id="animation">This animation explains how to use the boot menu key:</p>
 
 <video controls="true" width="640" height="360" poster="https://tails.boum.org/install/inc/videos/boot-menu-key.png">
   <source src="https://tails.boum.org/install/inc/videos/boot-menu-key.webm" type="video/webm" />