Fix reconnection handling in the chat demo app

[mixaildudin]

The kind of change this PR does introduce

• a bug fix
• a new feature
• an update to the documentation
• a code change that improves performance
• other

Current behavior

The source code of the example app examples/chat implies that reconnetion status (failure or success) is shown to the user.
In fact, it's not, because the reconnection events are listened to incorrectly: you're supposed to listen to the Manager's events like socket.io.on(...), not just socket.on(...).

I only wanted to take a look at how to handle disconnections and do reconnections, but here is what it came down to :)

New behavior

The example works as it's supposed to, you can now see messages like "attempt to reconnect has failed" in the UI.

Other information (e.g. related issues)

Also updated README in the example: it says you need to run npm ci to install packages, but since lockfiles are gitignored in the example folder, you actually need to run npm i

[darrachequesne]

Good catch, thanks 👍