Improve string comment.

    <!-- Label of the color mode widget. [CHAR LIMIT=20] -->

    <string name="label_color">Color</string>

    <!-- Label of the duplex mode widget. [CHAR LIMIT=20] -->

    <!-- Label of the printer mode to print on both sides of paper. [CHAR LIMIT=20] -->

    <string name="label_duplex">Two-sided</string>

    <!-- Label of the orientation widget. [CHAR LIMIT=20] -->