Clarify process_dex2oat_label description

    <string name="process_kernel_label">Android OS</string>

    <!-- Label for mediaserver process in battery usage -->

    <string name="process_mediaserver_label">Mediaserver</string>

    <!-- Label for dex2oat process used for app optimization in battery usage -->

    <!-- Label for dex2oat process in battery usage used for the optimization of one or more apps -->

    <string name="process_dex2oat_label">App optimization</string>

    <!-- [CHAR_LIMIT=40] Battery saver: Label for feature, title + menu item -->