doc: Fix directory structure for 'packages' dir

Indent the subdirectories a bit to get a better idea what they
should look like.

Change-Id: I0d4e4e32723e7e00148956123241ed4f818c16f3
Reviewed-by: Niels Weber <niels.weber@digia.com>
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>