DOC: Add entry for custom warnings in CHANGELOG.md

Added a placeholder in the [Unreleased] section for the upcoming feature
to add custom warnings when a rocket has no motors, parachute, or AeroSurface. See #285

Author: C8H10O2

CHANGELOG.md

@@ -31,6 +31,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 Attention: The newest changes should be on top -->
 
 ### Added
+- ENH: Custom Exception errors and messages [#285](https://github.com/RocketPy-Team/RocketPy/issues/285)
 - ENH: Tank Fluids with Variable Density from Temperature and Pressure [#852](https://github.com/RocketPy-Team/RocketPy/pull/852)
 - ENH: Controller (AirBrakes) and Sensors Encoding [#849](https://github.com/RocketPy-Team/RocketPy/pull/849)
 - EHN: Addition of ensemble variable to ECMWF dictionaries [#842](https://github.com/RocketPy-Team/RocketPy/pull/842)