Add better explanation of the `onLoad` engine handler.

docs/source/reference/lua-scripting/overview.rst

@@ -246,11 +246,14 @@ See :ref:`Engine handlers reference`.
 onSave and onLoad
 =================
 
-When a game is saved or loaded, the engine calls the engine handlers `onSave` or `onLoad` for every script.
+When a game is saved or loaded, the engine calls the engine handlers `onSave` or `onLoad` to save or load each script.
 The value that `onSave` returns will be passed to `onLoad` when the game is loaded.
 It is the only way to save the internal state of a script. All other script variables will be lost after closing the game.
 The saved state must be :ref:`serializable <Serializable data>`.
 
+Note that `onLoad` means loading a script rather than loading a game. During loading a game `onLoad` works only for the scripts that were already existed when the game was saved (i.e. present in the save file).
+If a completely new script was started (for example if it is a script of a newly installed mod) then the `onInit` handler is used even if it happened when loading a saved game.
+
 `onSave` and `onLoad` can be called even for objects in inactive state, so it shouldn't use `openmw.nearby`.
 
 An example: