Updated RELEASE_NOTES.

RELEASE_NOTES.md

@@ -4,6 +4,8 @@
 
 Users can now set the number of days after which the posts in their timeline will be deleted (this setting applies to both their own posts and those from the rest of the Fediverse).
 
+The `note` action from the command-line tool can also accept the post content from the standard input.
+
 ## 2.20
 
 Image attachments in posts can now have a description (a.k.a. "alt text").