add rationale to docs

[matthiasdebernardini]

I am curious what the main benefit to running this server instead of the default that axum crate uses.

Why should someone consider using this crate in their web API?

[programatik29]

Main reason is to use TLS easily and efficiently. Limitations of hyper::server::Server makes it really hard and tricky to efficiently use TLS. This crate solves the problem by providing alternative high level (hyper) server which has a different API.