Update example and docs

[thirtysixbananas]

This example failed. Looking at the code there's never any "excess", as the channel type is socketready = Channel{Tuple{IO, Response}}(0).

At first I thought this was just an outdated example, what confuses me is that from git blame I can't tell why someone thought there was an excess. Maybe it's just a mistake, as opposed to being out of date, or maybe I'm missing something.

Please review.

[thirtysixbananas]

I also suggest updating the url. The previous one returned 301 permanent redirect, so a user doesn't actually see the upgrade which is the point of the example.

Before:

HTTP/1.1 301 Moved Permanently
location: https://echo.websocket.org/
server: Fly/fbde0e6c3 (2025-12-17)
via: 1.1 fly.io
fly-request-id: 01KD2Z8F0ETXCGER8D9MG5HFF4-lhr
content-length: 0
date: Mon, 22 Dec 2025 12:06:31 GMT

After:

HTTP/1.1 101 Switching Protocols
upgrade: websocket
connection: Upgrade
sec-websocket-accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
date: Mon, 22 Dec 2025 12:06:57 GMT
server: Fly/fbde0e6c3 (2025-12-17)
via: 1.1 fly.io
fly-request-id: 01KD2Z976G0DZSQBX9KVN606CE-lhr