snippets: recovery_reboot: Clarify how to navigate fastboot menu

Change-Id: Iafe62a0acb325af329965d0284594ff2c57c33e7

Author: npjohnson

_includes/snippets/recovery_reboot.md

@@ -1,6 +1,7 @@
 {%- case device.recovery_reboot %}
 {%- when 'fastboot_menu' %}
 Use the menu to navigate to and to select the `Recovery` option.
+    {% include alerts/note.html content="Please note that on most devices you'll need to use the <kbd>Volume Buttons</kbd> to cycle onscreen options and the <kbd>Power Button</kbd> to select (Mobile), or by short pressing the <kbd>Side Button</kbd> to cycle onscreen options and by long pressing the <kbd>Side Button</kbd> to select (Android TV)." %}
 {%- when 'fastboot_boot' %}
 ```
 fastboot boot {{ device.recovery_partition_name }}.img