* Updated the README example with acquire connection
Initially from reading the docs and examples I tried to use `&mut pool` instead of `&mut conn`. The compiler gave me an error that `Pool<MySql>` didn't implement `Executor`. I had to do a bit of digging and eventually just viewed the source of `Pool` to find `acquire()`, `try_acquire()` etc.
I think this change makes it a bit easier for someone to get started.
* Update README.md to reference initial pool declaration
* Fixed compile issues and added examples of using &mut &pool