Add documentation for some common gps commands

        pw.println("    Sets the master location switch enabled state.");

        pw.println("  send-extra-command <PROVIDER> <COMMAND>");

        pw.println("    Sends the given extra command to the given provider.");

        pw.println();

        pw.println("    Common commands that may be supported by the gps provider, depending on");

        pw.println("    hardware and software configurations:");

        pw.println("      delete_aiding_data - requests deletion of any predictive aiding data");

        pw.println("      force_time_injection - requests NTP time injection to chipset");

        pw.println("      force_psds_injection - "

                + "requests predictive aiding data injection to chipset");

    }

}