Add Important note about Character component gravity override behavior (#422)

* Initial plan

* Add Important note about Character component gravity override behavior

Co-authored-by: VaclavElias <[email protected]>

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Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: VaclavElias <[email protected]>

en/manual/physics/characters.md

@@ -23,6 +23,9 @@ Have a look at the [API](xref:Stride.BepuPhysics.CharacterComponent) for more de
 
 ## Custom Character Controllers
 
+> [!IMPORTANT]
+> The `CharacterComponent`'s default `IsGrounded` handling temporarily overrides the `Gravity` flag: when the character is grounded and idle, `Gravity` is set to `false` to prevent sliding down slopes. If you need to disable or customize gravity (for flying characters or special movement modes), derive from `CharacterComponent` and adjust the update logic.
+
 When creating a controller, it is recommended to create a new class inheriting from this component instead of using it as is, you can access its internal state and override it with your own logic to better fit your game.
 
 ```cs