docs: Add documentation to setup some clients (more to follow)

docs/setup/client.md

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+# Client Setup
+
+## Common
+
+Following resources are available.
+
+```
+/.well-known/caldav
+# CalDAV root
+/caldav
+# Principal home
+/caldav/principal/<user_id>
+# Calendar home
+/caldav/principal/<user_id>/<calendar_id>
+/caldav/principal/<user_id>/_birthdays_<addressbook_id>
+```
+
+```
+/.well-known/carddav
+# CardDAV root
+/carddav
+# Principal home
+/carddav/principal/<user_id>
+# Addressbook home
+/carddav/principal/<user_id>/<addressbook_id>
+```
+
+### Authentication
+
+Authenticate with HTTP Basic authentication using your user id and a generated app token.
+
+## DAVx5
+
+You can set up DAVx5 through the Nextcloud login flow. Collections including group collections will automatically be discovered.
+
+## Apple Calendar
+
+You can download a configuration profile from the frontend in the app token section.
+
+**Limitation**: Group collections are not automatically discovered, for these you need to set up separate CalDAV configurations using the corresponding principal homes (but your own user id).
+
+## Evolution
+
+Set up a collection account in the account settings.
+
+**Limitation**: Group collections are not discovered. It seems as if currently you have to add each group collection manually.
+
+## Home Assistant CalDAV integration
+
+As URL specify
+
+```
+https://<your-host>/.well-known/caldav
+```
+
+For goup collections explicitly specify
+
+```
+https://<your-host>/caldav/principal/<principal>
+```