Add calendar sharing options

[mactrent]

Current docs show how to create, edit and subscribe. We could use an overview of sharing options.
Some notes:

• A single event can be shared by exporting it as a .ics file and sending that to the recipient
• Entire calendars can be shared with other Nextcloud users read-only or with write/edit access
  • Even though this looks similar to file sharing, this doesn't federate
• The 'Share link' option goes to a web viewer landing page
• The iCal subscription option is accessible from that page
  • This is the current way to share a calendar between instances

[skjnldsv]

@georgehrke

[georgehrke]

A single event can be shared by exporting it as a .ics file and sending that to the recipient

Well, it can also be shared by adding the sharee as an attendee.

Even though this looks similar to file sharing, this doesn't federate

Correct, there is a issue open about that in the server, but it was not implemented yet.

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We could use an overview of sharing options.

@mactrent Would you mind helping out here?
Contributing to our documentation is as easy as sending a pull-request.
This is the file in question: https://github.com/nextcloud/documentation/blob/master/user_manual/pim/calendar.rst