⭐ [Documentation] - Show how to share files when using a multi user server

[youngcw]

Description

The current documentation for multi user is pretty basic, but I think the only thing missing is how to share files between users.

It probably should be added under "Using Actual" -> "Managing Files"

Documentation URL

https://github.com/actualbudget/docs/blob/master/docs/getting-started/manage-files.md