Update RELEASE_NOTES.md

Author: emmadesilva

RELEASE_NOTES.md

@@ -19,6 +19,7 @@ This serves two purposes:
 - Added support for setting custom navigation items in the YAML configuration in https://github.com/hydephp/develop/pull/1818
 - Added support for setting extra attributes for navigation items in https://github.com/hydephp/develop/pull/1824
 - Introduced a new navigation config builder class to simplify navigation configuration in https://github.com/hydephp/develop/pull/1827
+- You can now add custom posts to the blog post feed component when including it directly in https://github.com/hydephp/develop/pull/1893
 
 ### Changed
 - **Breaking:** The internals of the navigation system has been rewritten into a new Navigation API. This change is breaking for custom navigation implementations. For more information, see below.