guile-clutter: some migration doc...

hello guilers,

although most of you probably are aware, here are 2 [old] pointers that might be
helpful to the process of porting guile-clutter from 0.8 to 1.0:

	http://lwn.net/Articles/345468/
	http://docs.clutter-project.org/docs/clutter/stable/migration.html

cheers,
david