Document the new `tests.helper.catch_warnings` context manager.
Document the new `tests.helper.catch_warnings` context manager.

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