Tweak the docs for the Inspect protocol
Tweak the docs for the Inspect protocol

The docs for the Inspect protocol mentioned that if there's an error
while inspecting a struct (for which the Inspect protocol has been
implemented), then the struct is printed with a raw representation.

This commit makes it clear that an `ArgumentError` is raised and the
struct is printed raw in the error message.

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