many changes

Author: furas

pygame/button-change-stage/README.md

@@ -1,7 +1,7 @@
 
 Using button to change `Stage`
 
-It uses `event.MOUSEBUTTONDOWN` instead of `mouse.get_pressed()` so it has no problem when buttons are in the same place.
+It uses [event.MOUSEBUTTONDOWN](http://pygame.org/docs/ref/event.html) instead of [mouse.get_pressed()](http://pygame.org/docs/ref/mouse.html#pygame.mouse.get_pressed) so it has no problem when buttons are in the same place.
 
 ![#1](images/pygame-stage1.png?raw=true)