Improve documentation for logger metadata
Improve documentation for logger metadata

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