Update release notes

Add a note about the removal of the `limit` attribute from
`Anycast` channel.

Signed-off-by: Daniel Zullo <daniel.zullo@frequenz.com>

RELEASE_NOTES.md

@@ -6,7 +6,7 @@ The `Timer` now can be started with a delay.
 
 ## Upgrading
 
-<!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
+* The `limit` attribute was removed from `Anycast` channel as the same information can be obtained from its buffer through `deque.maxlen` property.
 
 ## New Features