Update basic.md

[aaronpkelly]

The full example has at https://github.com/hyperium/hyper/blob/master/examples/client.rs will not compile straight away, as it has an additional dependency which is not mentioned in the guide

[tobymurray]

As a new user, I also ran into this. I started with the documentation, appreciated the fork between "client" and "server, went to https://hyper.rs/guides/client/basic/ and then to the "full example" which failed to compile. It is not intuitive that the dependencies for the example I was just reading are different than the dependencies for the example I'm lead to, so my first experience with this library was:

error[E0433]: failed to resolve: use of undeclared type or module `pretty_env_logger`
  --> src/main.rs:11:5
   |
11 |     pretty_env_logger::init();
   |     ^^^^^^^^^^^^^^^^^ use of undeclared type or module `pretty_env_logger`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0433`.

Whether this is updated as described in the pull request or reworked to make it more clear, I think it's worthwhile to change something so there's as little friction as possible on new user flow.