WP dashboard notification sample for functions.php

index.php

// Place admin message about the Carousel Video and Carousel categories
function pz_carousel_admin_notice() {
	if ( is_admin() ) {
		if ( in_category('Carousel Video') ) {
			$class = 'video-carousel-notice notice notice-info is-dismissible';
			$message = __( 'Video Carousel posts are ordered by most recently updated to least. They display on the homepage', 'sample-text-domain' );
			printf( '<div class="%1$s"><p>%2$s</p></div>', esc_attr( $class ), esc_html( $message ) ); 
		}

		if ( in_category('Carousel') ) {
			$class = 'slide-carousel-notice notice notice-info is-dismissible';
			$message = __( 'Carousel posts are ordered by most recently updated to least. They display on the homepage', 'sample-text-domain' );
			printf( '<div class="%1$s"><p>%2$s</p></div>', esc_attr( $class ), esc_html( $message ) ); 
		}
	}

}
add_action( 'admin_notices', 'pz_carousel_admin_notice' );