add link for ar300m16 boot_dev switch (#316)

arednGettingStarted/installing_firmware.rst

@@ -330,7 +330,7 @@ Download the *Install Checklist* for GL-iNet devices. These devices allow you to
 
 After the GL-iNet device is first booted and configured, navigate to the **Upgrade** section and click *Local Upgrade* to select the AREDN |trade| *sysupgrade.bin* file you downloaded for your device.
 
-.. attention:: Be sure to uncheck the **Keep Settings** checkbox, since GL.iNet settings are incompatible with AREDN |trade| firmware.
+.. attention:: Be sure to uncheck the **Keep Settings** checkbox, since GL.iNet settings are incompatible with AREDN |trade| firmware. Also, the AR300M16 devices may have a *boot_dev* switch, so be sure to read the `GL.iNet boot documentation <https://docs.gl-inet.com/router/en/3/specification/gl-ar300m/#control-which-firmware-you-are-booting-into>`_ to select the correct boot mode.
 
 The node will automatically reboot with the new AREDN |trade| firmware image. If for some reason your GL-iNet device gets into an unusable state, you should be able to recover using the process documented here:
 `GL-iNet debrick procedure <https://docs.gl-inet.com/en/3/tutorials/debrick/>`_