Add recommendation on using OAuth and app passwords

Author: sunkup

introduction.rst

@@ -36,13 +36,17 @@ How to start using DAVx⁵ on your Android device:
 #. Open DAVx⁵.
 #. Follow the instructions of the start screen (permissions, battery saving etc.).
 #. Tap on "⊕ Add account" to add a new account.
-#. Enter your base URL / email address and login credentials.
+#. Login using OAuth (preferred if supported) or base URL / email address and login credentials.
    You can get the base URL from your service provider and/or our `list of tested services <https://www.davx5.com/tested-with/>`_.
 #. Finish the steps to add the account.
 #. Select the address books and calendars/task lists you want to synchronize so that the respective switches are enabled.
 #. Force sync ("🗘 Synchronize") if you want the data to be available immediately.
 #. Access your address books, events and tasks using your favorite apps (Contacts, Calendar, OpenTasks, …).
 
+If your provider doesn't support OAuth login, we strongly recommend using app passwords with DAVx⁵,
+if available. Using a dedicated app password for each app — like DAVx⁵ — keeps your main account
+password private and allows you to revoke access at any time.
+
 When you create a contact/event, select the desired DAVx⁵ account as storage location.
 Local contacts/events will stay on your phone and not be synchronized. If you're using DAVx⁵ the first time, you may
 want to :faq:`transfer your local contacts to the CardDAV server <existing-contacts-are-not-synced>`.