docs: adding examples and a see link to Websockets jdocs

[thisisjofrank]

adding examples to websockets interfaces and a see link

[ry]

this isn't very descriptive - you could give some examples of extensions that might be returned

[thisisjofrank]

updated

[ry]

There's no such thing as WebSocketServer. The example doesn't need to be runnable - just looking for a description of what this is... something like

/**
 * Returns the extensions selected by the server, if any.
 *
 * WebSocket extensions add optional features negotiated during the handshake via
 * the `Sec-WebSocket-Extensions` header.
 *
 * At the time of writing, there are two registered extensions:
 *
 * - [`permessage-deflate`](https://www.rfc-editor.org/rfc/rfc7692.html): Enables per-message compression using DEFLATE.
 * - [`bbf-usp-protocol`](https://usp.technology/): Used by the Broadband Forum's User Services Platform (USP).
 *
 * See the full list at [IANA WebSocket Extensions](https://www.iana.org/assignments/websocket/websocket.xml#extension-name).
 *
 * Example:
 *
 * ```ts
 * const ws = new WebSocket("ws://localhost:8080");
 * console.log(ws.extensions); // e.g., "permessage-deflate"
 * ```
 */
readonly extensions: string;