Update README.md: added hyper-util to the dependencies section

There is a need to include the hyper-util crate to compile examples, otherwise, it cannot solve the dependency for TokioIo. 
It looks like the examples also need to be updated as they refer to an internal "../benches/support/mod.rs" for TokioIo

examples/README.md

@@ -22,6 +22,7 @@ serde_json = "1.0"
 form_urlencoded = "1"
 http = "1"
 futures-util = { version = "0.3", default-features = false }
+hyper-util = { version = "0.1", features = ["full"] }
 ```
 
 ## Getting Started