dropbox docs: explain team folders (#339)

Author: mifi

docs/sources/companion-plugins/dropbox.mdx

@@ -127,6 +127,10 @@ Things to note:
 - Choose the “Dropbox API”, not the business variant.
 - Typically you’ll want “Full Dropbox” access, unless you are absolutely certain
   that you need the other one.
+- Enable the scopes `account_info.read`, `files.metadata.read` and
+  `files.content.read` under “Permissions”. If you want to support
+  [Team folders / Teams spaces](https://developers.dropbox.com/dbx-team-files-guide),
+  counterintuitively you must **not** enable any Team scopes.
 
 You’ll be redirected to the app page. This page lists the app key and app
 secret, which you should use to configure Companion as shown above.