Update building_os.md

I use a VM for my ubuntu server and so awkward to plug in my SD card and mount to the VM. Wanted the image so burn to multiple SD card aswell

pages/building_os.md

@@ -67,11 +67,17 @@ The Pi-KVM OS is based on Arch Linux ARM and contains all the required packages
     [user@localhost os]$ make os
     ```
     
-5. Put SD card into card reader and install OS (**you should disable automounting beforehand**: `systemctl stop udisk2` or something like that):
+5a. Put SD card into card reader and install OS (**you should disable automounting beforehand**: `systemctl stop udisk2` or something like that):
     ```shell
     [user@localhost os]$ make install
     ```
-    
+
+5b. Make the image to copy elsewhere and burn on to SD
+    ```shell
+    [user@localhost os]$ make image
+    ```
+    Image is then available as a bziped file in images/
+
 6. After installation remove the SD card and insert it into your RPi. Turn on the power. The RPi will try to get an IP address using DHCP on your LAN. It will then be available via SSH.
 
 7. If you can't find the device's address, try using the following command: