Add mention of not adding .dev
Add mention of not adding .dev

as discussed in #5600

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