fixed sectioning in install.rst
fixed sectioning in install.rst

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