Add documentation for angles_dimensionless in units/equivalencies.rst
Add documentation for angles_dimensionless in units/equivalencies.rst

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