Add synopsis to the UI

[kirilknysh]

It may be useful to have some brief description on the page. Smth like a brief explanation on how to create the connection, e.g.

const ws = new WebSocket(`ws://${window.location.host}`);
ws.onopen = () => {};
ws.onmessage = () => {};

Perhaps, make an expandable instructions from https://github.com/21-23/wsc#solving-the-challenge to not switch between tabs.