Update release notes

Signed-off-by: Sahas Subramanian <sahas.subramanian@proton.me>

Author: shsms

RELEASE_NOTES.md

@@ -11,7 +11,9 @@
 
 ## New Features
 
-<!-- Here goes the main new features and examples or instructions on how to use them -->
+- There's a new `Oneshot` channel, which returns a sender and a receiver.  A single message can be sent using the sender, after which it will be closed.  And the receiver will close as soon as the message is received.
+
+- `Sender`s now have an `aclose`, which must be called, when they are no-longer needed.
 
 ## Bug Fixes