Improve docs for custom formatting
Improve docs for custom formatting

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