doc: add additional explanation to the wildcard section in permissions

Co-authored-by: Rafael Gonzaga <rafael.nunu@hotmail.com>
PR-URL: nodejs#53664
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Marco Ippolito <marcoippolito54@gmail.com>

Author: jakecastelli

doc/api/permissions.md

@@ -563,6 +563,14 @@ Wildcards are supported too:
 After passing a wildcard character (`*`) all subsequent characters will
 be ignored. For example: `/home/*.js` will work similar to `/home/*`.
 
+When the permission model is initialized, it will automatically add a wildcard
+(\*) if the specified directory exists. For example, if `/home/test/files`
+exists, it will be treated as `/home/test/files/*`. However, if the directory
+does not exist, the wildcard will not be added, and access will be limited to
+`/home/test/files`. If you want to allow access to a folder that does not exist
+yet, make sure to explicitly include the wildcard:
+`/my-path/folder-do-not-exist/*`.
+
 #### Permission Model constraints
 
 There are constraints you need to know before using this system: