add a docstring for test_photometric pointing to test_logarithmic
add a docstring for test_photometric pointing to test_logarithmic

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