Added example querying an unbound type variable

[niksilver]

The error message says:

-- UNBOUND TYPE VARIABLE ---------------------------------- typo-not-unbound.elm

The `Counter` type alias uses an unbound type variable `int` in its definition:

1| type alias Counter =
2|   { i : int }
           ^^^
You probably need to change the declaration to something like this:

    type alias Counter int = ...

Maybe it is an unbound type variable. But maybe I just made a typo and should have used a
capital letter.

This won't just happen with builtin types, of course. In my own application
I defined my own type called Column and got the above error when I mistyped it as column.