Update README to mention only: and except: for require
Update README to mention only: and except: for require

joshprice/elixir,gfvcastro/elixir,lexmag/elixir,gfvcastro/elixir,kimshrier/elixir,kelvinst/elixir,ggcampinho/elixir,pedrosnk/elixir,beedub/elixir,ggcampinho/elixir,michalmuskala/elixir,kelvinst/elixir,antipax/elixir,antipax/elixir,elixir-lang/elixir,beedub/elixir,pedrosnk/elixir,kimshrier/elixir,lexmag/elixir