add clarifying comment justifying imshow_only_kwargs
add clarifying comment justifying imshow_only_kwargs

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