Expand description of `allow_local_remote_servers`

Thanks for helping improve our documentation!

• There is always room for improvement!
• All contributions (changes and change ideas) - from the largest to the tiniest - help make Nextcloud better and easier to use!

Came up on the forum: https://help.nextcloud.com/t/what-does-allow-local-remote-servers-do/188618

Notes

• Please be patient: this is a large open source project that is overseen by a mixture of volunteers and non-volunteers which are all ultimately busy.
• If your suggestion is a troubleshooting scenario or one you're not 100% certain about, please post for feedback on the Nextcloud Help Forum first.
  • Then return here to bring back your experience to help improve the documentation for clarity, etc. (and link back to the forum discussion in your report!)

Protip: If you want to help move things along (or just help out in other ways too) here are some suggestions:

• Look for areas where you can assist - even seemingly unrelated areas - because doing so frees up resources for your favorite topics and ideas.
• Submit a proposed change - that attempts to addresses your issue - as a pull request.
• Participate in a discussion on some other unresolved submitted idea ("issues") to help move it along.
• Post a comment or review on someone else's proposed change ("pull request") to help move it along.

Start with the linked Nextcloud Help Forum discussion to understand what allow_local_remote_servers does and what explanation is missing. Locate the existing documentation for this setting, then expand it so the behavior is clear and the forum question is addressed.