add howto regarding MFA

.gitignore

@@ -0,0 +1 @@
+.DS_Store

_toc.yml

@@ -10,6 +10,7 @@ chapters:
   - file: user-guide/index
     sections:
       - file: user-guide/login_servers
+      - file: user-guide/MFA
       - file: user-guide/ms_teams
       - file: user-guide/evolution_for_o365
       - file: user-guide/thunderbird_for_o365

user-guide/MFA.md

@@ -0,0 +1,35 @@
+# MFA - Multi Factor Authentication
+
+PSI multi factor authentication is based on a Microsoft Authenticatior infrastructure.
+
+This is how you can configure our account so that you are able to use any OTP instead of Microsoft Authenticator.
+
+1. Login to:
+
+https://mysignins.microsoft.com/security-info
+
+2. Click on Add Authentication Method
+![Alt text](MFA_1.png)
+
+3. Select Authenticator-App and click __Add__
+![Alt text](MFA_2.png)
+
+4. When you get this menu - click on the link __I want to add an other Authenticator-App__ (do NOT click on _Continue_)
+![Alt text](MFA_3.png)
+
+5. The dialog will then change to something like this. Now click on _Continue_.
+![Alt text](MFA_4.png)
+
+6. You will then have a QR code presented that you have to scan with your Authenticator app. 
+![Alt text](MFA_7.png)
+
+7. Verify the correct setup by entering an OTP code:
+![Alt text](MFA_5.png)
+
+8. Continue the dialog to finish adding the method.
+
+
+
+If you want to set OTP based authentication as default change the Standard Authentication Method to "Authenticator-App or Hardwaretoken - Code"
+
+![Alt text](MFA_6.png)