script, docs: Update documentation for alphas
script, docs: Update documentation for alphas

It is now possible to have Alpha instances defined explicitly for
behaviours, so we need to fix the documentation.

collects/clutter,kerrickstaley/clutter-vala,collects/clutter,dlespiau/clutter,GNOME/clutter,heysion/clutter-clone,spatulasnout/clutter,spatulasnout/clutter,djdeath/clutter-multithreaded,djdeath/clutter-multithreaded,nobled/clutter,djdeath/clutter-multithreaded,GNOME/clutter,ebassi/clutter,collects/clutter,heysion/clutter-clone,jigpu/clutter,djdeath/clutter,djdeath/clutter-android,nobled/clutter,spatulasnout/clutter,Distrotech/clutter,ebassi/clutter,djdeath/clutter-multithreaded,rkudiyarov/clutter_osx,dlespiau/clutter,jigpu/clutter,jigpu/clutter,Distrotech/clutter,jigpu/clutter,rkudiyarov/clutter_osx,djdeath/clutter-android,Distrotech/clutter,ebassi/clutter,Distrotech/clutter,jigpu/clutter,rkudiyarov/clutter_osx,nobled/clutter,kerrickstaley/clutter-vala,djdeath/clutter,collects/clutter,jigpu/clutter,djdeath/clutter,djdeath/clutter-android,djdeath/clutter,djdeath/clutter,kerrickstaley/clutter-vala,GNOME/clutter,djdeath/clutter,Distrotech/clutter,heysion/clutter-clone,collects/clutter,kerrickstaley/clutter-vala,GNOME/clutter,rkudiyarov/clutter_osx,djdeath/clutter-android,dlespiau/clutter,spatulasnout/clutter,heysion/clutter-clone,djdeath/clutter-android,spatulasnout/clutter,heysion/clutter-clone,ebassi/clutter,ebassi/clutter,GNOME/clutter,Distrotech/clutter