Category Article Pro
This Plugin Adds Advanced Category Article Field in Category Editor of WordPress, it also Support Custom Taxonomies for default post types (i.e. tags, terms)
Why add content to category pages
Without unique, useful content a category page is really just a list of posts, each with a small amount of content that is duplicated on the actual post page itself. All other things being equal, a category page with unique, useful content is going to out-rank one without it. Furthermore, the content at the top of the page can help user visitors through the conversion funnel, help answer common questions, and offer an opportunity to introduce your branding and voice.
What type of content to put on category pages
One word: Useful. What you want to do here is answer common questions and instruct the visitor on what to do next. Explain the difference between major brands, or call out the most popular models. Do not simply write filler copy for search engines. And, above all, do not just write a generic description that goes on all category pages, even if you dynamically change the category name.