added .gitignore to ignore docs _build
added .gitignore to ignore docs _build

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