Add 3.3.1 release notes

source/releasenotes/3.3.1.rst

+3.3.1 (2023-07-11)
+==================
+
+First patch release of the 3.3.x series.
+
+Changes
+-------
+
+Here is the complete changelog of this version:
+
+- director: Max delay between attempts and delay increase factor can now be
+  changed in a Actor config with the following entries:
+
+  - ``xbus.director.delay.max``: a duration. Accepted units are 'ms', 's', 'm', 'h'
+
+  - ``xbus.director.delay.increase-factor``: a increase factor. Can be expressed
+    as a percentage as in "50%", or a floating point number as in "0.5".
+
+- Fix: Canceling a process now properly unshedule jobs that are waiting for a 
+  new attempt after a TooBusy error.
+
+- api: implement 'Actor.Create'. The API existed already but was never
+  implemented.
+