Code Tricks have an article on this.
The article is so short that quoting it will essentially copy it:
//URL to fetch RSS feeds for custom post type feeds.
www.your-website.com/feed/?post_type=custom_post_type_name
//URL to fetch RSS feed for custom post type feeds including the custom taxonomy.
www.your-website.com/feed/?post_type=custom_post_type_name&taxonomy_name=taxonomy
//This is just an example.
www.code-tricks.com/feed/?post_type=tutorials&tutorials_category=javascript
Please do see the original article.