two factor auth - generate(and use) an app password adding NC calendar to Thunderbird

[Salzorian]

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Please add a hint to generate(and use) an app password if one wants to add a Nextcloud calendar to thunderbird and activated two factor auth.
Toke me a while to find out. :)

I refer to following howto
-->
https://docs.nextcloud.com/server/latest/user_manual/en/groupware/sync_thunderbird.html

Thx

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[tflidd]

I added a Note box similar to this page:
https://docs.nextcloud.com/server/stable/user_manual/en/files/access_webdav.html

In pull request #12465