quickstart: add a comment about other (remote) filesystems

docs/quickstart.rst

@@ -263,3 +263,7 @@ mounting the remote filesystem, for example, using sshfs::
   $ sshfs user@hostname:/path/to /path/to
   $ borg init /path/to/repo
   $ fusermount -u /path/to
+
+You can also use other remote filesystems in a similar way. Just be careful,
+not all filesystems out there are really stable and working good enough to
+be acceptable for backup usage.