Update CHANGELOG.md

CHANGELOG.md

 # Changelog
 
-## [Unreleased]
+## [0.4.0] - 2023-03-24 
 
 ### Added
 
@@ -14,6 +14,7 @@
 - Deprecated `VariableStepGuppyEnv` (use `ConfigurableGuppyEnv` instead, do not use variable step length.)
 - Deprecated `AdaptiveAgent` and related functions (unmaintained and untested)
 - Deprecated built-in Couzin guppies (use `LiveFemaleFemaleConstantSpeedCouzinModel` from `fish_models` instead)
+- Providing `controller_params` is now obligatory for robots that use PID controller simulation
 
 ## [0.3.0] - 2022-10-14
 
@@ -52,4 +53,4 @@
 ### Changed
 
 - Deprecated MXNetGuppy
-- Fixed various small bugs
\ No newline at end of file
+- Fixed various small bugs