Starting a kernel

I’m experimenting with `aleph.sagemath.org` and have a trouble with a kernel start. It’s more a documentation issue I think.

Wiki tells me to make a `POST` request to a `/kernel` path to start a kernel. But it doesn’t work, you could try it using `curl`:

```console
$ curl -X POST -H "Accept: application/json" http://aleph.sagemath.org/kernel
```

I get `400: Bad Request` response.

If I look at a network usage via Chromium tools I see that “Evaluate” button sends request to such URL: `http://aleph.sagemath.org/kernel?notebook=398150C123E04F3683B9930F8A6EE604`. If you’ll use it with `curl` response would be fine.

What does `notebook` parameter mean and how should I generate it’s value?