Update parallel compiler callback documentation
Update parallel compiler callback documentation

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