Improve documentation

Author: martinRenou

docs/source/events.rst

@@ -1,10 +1,12 @@
 Interactions
 ============
 
-Using built-in events
+Built-in mouse events
 ---------------------
 
-The following built-in mouse events are supported: ``mouse_down``, ``mouse_move``, ``mouse_up`` and ``mouse_out``.
+The following built-in mouse events are supported: ``mouse_down``, ``mouse_move``, ``mouse_up`` and ``mouse_out``. You can define Python callback functions that will be called whenever those mouse events occur, using the ``on_mouse_down``, ``on_mouse_move``, ``on_mouse_up`` and ``on_mouse_out`` methods.
+
+Those methods take a callback function as single argument, this callback function must take two positional arguments that are the ``x`` and ``y`` pixel coordinates where the mouse was during the event.
 
 .. code:: Python
 
@@ -23,8 +25,8 @@ The following built-in mouse events are supported: ``mouse_down``, ``mouse_move`
 .. note::
     Please open an issue or a Pull Request if you want more events to be supported by ipycanvas
 
-Using ipyevents
----------------
+ipyevents
+---------
 
 If built-in events are not enough for your use case, you can use `ipyevents <https://github.com/mwcraig/ipyevents>`_ which provides mouse and keyboard events.