Add some more detail to System.cmd arguments documentation.
Add some more detail to System.cmd arguments documentation.

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