add yubikey screenshots for ios and desktop

_articles/account/setup-two-step-login-yubikey.md

@@ -54,12 +54,18 @@ Two-step login can permanently lock you out of your account. It is very importan
    Web
    {% image two-step/yubikey/web.png %}
 
+   Desktop
+   {% image two-step/yubikey/desktop.png %}
+
    Browser extension
    {% image two-step/yubikey/browser.png %}
 
    Android
    {% image two-step/yubikey/android.png %}
 
+   iOS
+   {% image two-step/yubikey/ios.png %}
+
 ## Android
 
 If you are having trouble getting the YubiKey NEO to work on your Android device, confirm the following: