altered docs 'make clean' command to also clean generated stuff
altered docs 'make clean' command to also clean generated stuff

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