Readme keep unread function

https://github.com/FreshRSS/FreshRSS/pull/1327

CHANGELOG.md

@@ -9,6 +9,7 @@
 	* New client supporting FreshRSS on Linux: FeedReader 2.0+ [#1252](https://github.com/FreshRSS/FreshRSS/issues/1252)
 * Features
 	* Rework the “mark as read during scroll” option, enabled by default for new users [#1258](https://github.com/FreshRSS/FreshRSS/issues/1258), [#1309](https://github.com/FreshRSS/FreshRSS/pull/1309)
+		* Including a *keep unread* function [#1327](https://github.com/FreshRSS/FreshRSS/pull/1327)
 	* In a multi-user context, take better advantage of other users’ refreshes [#1280](https://github.com/FreshRSS/FreshRSS/pull/1280)
 	* Better control of number of entries per page or RSS feed [#1249](https://github.com/FreshRSS/FreshRSS/issues/1249)
 		* Since X hours: `https://freshrss.example/i/?a=rss&hours=3`