fix: mistake in docs, change "multi-consumer" to "single-consumer"

[bajpai244]

I was following the content on channels, and there seems to be a mistake:

We seem to be talking about "multi-producer single-consumer"(mpsc) but have mentioned "multi-producer multi-consumer"(broadcast channels) instead!

NOTE: if this is replicated anywhere else, then we should fix that as well!

[Darksonn]

No, it is mentioned here because it supports multiple consumers. With async-channel, you can clone the receiver. However, unlike a broadcast channel, each message goes to only one receiver.

[bajpai244]

Oh! Gotcha!

Closing this then :)