Add documentation for new API key argument
Add documentation for new API key argument

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