BGE Python API: Completing doc for bge.types.KX_FontObject

This adds description of the Font object and about its (only one)
attribute, as well as an example of use.

Reviewers: campbellbarton, fsiddi, dfelinto, moguri

Reviewed By: dfelinto

Subscribers: lordloki

Projects: #documentation, #game_engine

Differential Revision: https://developer.blender.org/D863

doc/python_api/rst/bge_types/bge.types.KX_FontObject.rst

@@ -7,6 +7,26 @@ base class --- :class:`KX_GameObject`
 
 .. class:: KX_FontObject(KX_GameObject)
 
-   TODO.
+   A Font object.
 
+   .. code-block:: python
+
+      # Display a message about the exit key using a Font object.
+      import bge
+
+      co = bge.logic.getCurrentController()
+      font = co.owner
+
+      exit_key = bge.events.EventToString(bge.logic.getExitKey())
+
+      if exit_key.endswith("KEY"):
+          exit_key = exit_key[:-3]
+
+      font.text = "Press key '%s' to quit the game." % exit_key
+
+   .. attribute:: text
+
+      The text displayed by this Font object.
+
+      :type: string