Prasanna SP

Just like the normal WordPress site feed, wordpress categories and tags also has feeds. The category feed is located at <code>site.url/category/categoryname/feed</code>. This plugin automatically adds the RSS feed link to the current post categories after the post content. By default the plugin shows category feed link on single posts. You can change it’s settings to show it on other pages, such as archives as well. You can change it’s title in WP-Admin –> Settings –> Follow Category Feeds.
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Follow WordPress Category Feeds

This plugin adds link for the category feeds after post content.

antonpug

This plugin adds a customizable Better Follow Button at bottom right corner of your Jetpack-powered WordPress.org site.
The plugins integrates with the built in subscription manager of the Jetpack Plugin to collect the email of the subscriber and handle distribution of new posts via email.
NOTE: This plugin requires the Jetpack plugin to be installed & activated
For further information visit the plugin website.

Better Follow Button for Jetpack

Adds a floating subscription button (like on WordPress.com sites) to Jetpack-powered WordPress.org sites.

Follow WordPress Category Feeds vs Better Follow Button for Jetpack