Update boot-menu.md

Added link to open firmware models page for convenience

Author: AlexisSweetMcKay

content/boot-menu.md

@@ -25,6 +25,7 @@ The BIOS or boot menu can be accessed by holding specific keys down during boot.
 | Older laptops                                               | Depends on the system | F1                   |
 | Thelio desktops                                             | Del      | F8/F11/F12                         |
 | Meerkat (mini) desktops                                     | F2       | F10                               |
+![Open Firmware Models](https://support.system76.com/articles/open-firmware-systems/)
 
 ## Open Firmware Screenshots