readme.md example uses feature of crate that no longer exists

[FantasyPvP]

am i blind or does this just not exist in the crate anymore?

use yew_websocket::macros::Json;

also the example just straight up doesnt work in the latest version of yew without it.

[darioalessandro]

try this example https://github.com/security-union/yew-websocket/blob/master/examples/websocket-demo/src/main.rs

care to play a quick PR to fix this?