add mikrotik protected routerboot info

arednGettingStarted/installing_firmware.rst

@@ -186,6 +186,12 @@ Mikrotik devices require a **two-part install** process: First, boot the correct
 
 Mikrotik devices have a built-in `PXE <https://en.wikipedia.org/wiki/Preboot_Execution_Environment>`_ *client* which allows them to download a boot image from an external source. You will need to install and configure a `PXE <https://en.wikipedia.org/wiki/Preboot_Execution_Environment>`_ *server* on your Windows computer. The example below uses *Tiny PXE*. For more information, see the **Tools for Your Computer** section above.
 
+For most Mikrotik devices the steps below will work without issue. However, if your Mikrotik device has "Protected Routerboot" enabled, then you will need to disable it before proceeding. Use the manufacturer's instructions to connect to your device and display the RouterOS web interface. Navigate to the *System > Routerboard* section and uncheck or deselect "Protected Routerboot" as shown in the example below, then click the *Apply* button. You should now be able to power down the device and continue with the steps in the AREDN |trade| firmware install checklist.
+
+.. image:: _images/mikrotik-protectboot.png
+  :alt: Uncheck Mikrotik Protected Boot
+  :align: center
+
 Preparation
   - Download *both* of the appropriate Mikrotik *factory* and *sysupgrade* files from the AREDN |trade| website. Rename the initramfs-kernel file to ``rb.elf`` and keep the *sysupgrade* **bin** file available for later.