Updated RELEASE_NOTES.

RELEASE_NOTES.md

@@ -18,6 +18,8 @@ Renamed command-line actions `create_list` to `list_create` and `delete_list` to
 
 The default favicon URL can be changed from the server configuration.
 
+New command-line option `export_posts`, to export all posts by a user in a JSON format compatible with the one generated by Mastodon.
+
 ## 2.78
 
 Hashtag following also allow URLs to RSS feeds of ActivityPub objects (like e.g. https://mastodon.social/tags/ThankYouTuesday).