Always add category feed links

category-feed-links.php

<?php
/* Plugin Name: T5 Category Feed Links */

add_action( 'wp_head', function() {

	$cats = get_categories();
	$html = '<link rel="alternate" type="%1$s" title="Category %2$s" href="%3$s" />';
	$type = feed_content_type();

	foreach ( $cats as $cat ) {

		if ( 1 > $cat->count )
			continue;

		$title = esc_attr( $cat->name );
		$url = esc_url( get_category_feed_link( $cat->cat_ID ) );

		printf( $html, $type, $title, $url );
	}
});