Added link to doku page to welcome mail

uffd/selfservice/templates/newuser.mail.txt

@@ -4,6 +4,8 @@ welcome to the CCCV infrastructure.
 An account was created for you, visit this url to set your password: {{ url_for('selfservice.token_password', token=token, _external=True) }}
 **Please note this link is only valid for 48h**
 
+You can find more information here: https://docs.cccv.de/
+
 If you have no idea why someone would create an account for you to be used for the next CCC event organization, please contact it@cccv.de.
 
 Kind regards,