document None and list behavior for decorator
document None and list behavior for decorator

saimn/astropy,StuartLittlefair/astropy,dhomeier/astropy,larrybradley/astropy,saimn/astropy,lpsinger/astropy,pllim/astropy,astropy/astropy,kelle/astropy,astropy/astropy,DougBurke/astropy,dhomeier/astropy,AustereCuriosity/astropy,kelle/astropy,lpsinger/astropy,stargaser/astropy,aleksandr-bakanov/astropy,astropy/astropy,stargaser/astropy,DougBurke/astropy,mhvk/astropy,aleksandr-bakanov/astropy,stargaser/astropy,funbaker/astropy,bsipocz/astropy,kelle/astropy,saimn/astropy,mhvk/astropy,StuartLittlefair/astropy,StuartLittlefair/astropy,saimn/astropy,StuartLittlefair/astropy,lpsinger/astropy,saimn/astropy,bsipocz/astropy,DougBurke/astropy,kelle/astropy,MSeifert04/astropy,lpsinger/astropy,mhvk/astropy,kelle/astropy,funbaker/astropy,dhomeier/astropy,MSeifert04/astropy,pllim/astropy,pllim/astropy,astropy/astropy,bsipocz/astropy,larrybradley/astropy,mhvk/astropy,funbaker/astropy,aleksandr-bakanov/astropy,larrybradley/astropy,aleksandr-bakanov/astropy,funbaker/astropy,AustereCuriosity/astropy,DougBurke/astropy,mhvk/astropy,AustereCuriosity/astropy,AustereCuriosity/astropy,StuartLittlefair/astropy,bsipocz/astropy,larrybradley/astropy,lpsinger/astropy,pllim/astropy,MSeifert04/astropy,pllim/astropy,larrybradley/astropy,MSeifert04/astropy,dhomeier/astropy,stargaser/astropy,astropy/astropy,AustereCuriosity/astropy,dhomeier/astropy