docs: update Example server

[ghost]

Motivation

Hey! I want to try in helping out with #509.

the current example was just building the service without a loop to listen for requests. I wanted to fix this so new users can copy-paste a working server right away.

Solution

To make this, I:

• I incorporated the minimal server logic from @jplatte own caniuse.rs that are referenced in: here.
• I added hyper to the dev-dependencies and toggled on the service and server features for hyper-util.
• I ran cargo test --doc locally, and it's all green lights!

[jplatte]

Thanks!