Add first draft of plugin API description

[connman] / src / connman.conf

<!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
 "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
<busconfig>
    <policy user="root">
        <allow own="org.freedesktop.connman"/>
    </policy>
    <policy at_console="true">
        <allow send_interface="org.freedesktop.connman"/>
        <allow send_destination="org.freedesktop.connman"/>
    </policy>
</busconfig>