Document the return value and any exceptions thrown by basic/publish

[marcomorain]

Hi there 👋

The docs for basic/publish don't mention the return value or exceptions thrown.

Since basic/publish delegates to com.rabbitmq.client.Channel.basicPublish I believe that the function return nil (since the signature is void in Java, and it throws IOException if an error is encountered.

[michaelklishin]

Correct. Feel free to submit a PR for languor.docs, mention publisher confirms and then update the publishers/exchanges guide.