PyDoc: Merge manual docs for bge.texture

https://docs.blender.org/manual/en/dev/game_engine/python_api/videotexture.html

Had a few things that this file did not while this file having things the other did not.
To fix, I merged both documents into the python api.

doc/python_api/examples/bge.texture.py

@@ -1,8 +1,11 @@
 """
 Basic Video Playback
 ++++++++++++++++++++
-Example of how to replace a texture in game with a video. It needs to run
-everyframe.
+Example of how to replace a texture in game with a video.
+It needs to run everyframe.
+To avoid any confusion with the location of the file,
+we will use ``GameLogic.expandPath()`` to build an absolute file name,
+assuming the video file is in the same directory as the blend-file.
 """
 import bge
 from bge import texture
@@ -26,8 +29,18 @@ if not hasattr(logic, 'video'):
     logic.video.source = texture.VideoFFmpeg(movie)
     logic.video.source.scale = True
 
+    # Note that we can change the ``Texture`` source at any time.
+    # Suppose we want to switch between two movies during the game:
+    logic.mySources[0] = texture.VideoFFmpeg('movie1.avi')
+    logic.mySources[1] = texture.VideoFFmpeg('movie2.avi')
+
+    #And then assign (and reassign) the source during the game
+    logic.video.source = logic.mySources[movieSel]
+
     # quick off the movie, but it wont play in the background
     logic.video.source.play()
 
-# you need to call this function every frame to ensure update of the texture.
+
+# Video playback is not a background process: it happens only when we refresh the texture.
+# So you need to call this function every frame to ensure update of the texture.
 logic.video.refresh(True)