Update Release Notes

Signed-off-by: camille-bouvy-frequenz <[email protected]>

Author: camille-bouvy-frequenz

RELEASE_NOTES.md

@@ -15,6 +15,7 @@
 * Add more edge cases to the integration tests.
 * Add idiomatic string representations for `Power` and `Price` classes.
 * Add support for timeouts in the gRPC function calls
+* Export Client constants for external use
 
 ## Bug Fixes