Docs for Channel

The documentation for Channel is currently no more than intellisense can tell me (except which framework versions it applies to...), which is not enough for a documentation page: https://docs.microsoft.com/en-us/dotnet/api/system.threading.channels.channel-2

Channel and Channel aren't that important here, since Channel is just for constructing channels and Channel is just Channel.

The big one should have at least some description and a simple example. I haven't fully understood the whole blog post yet, but things like

"A channel is basically a data structure that’s used to store produced data for a consumer to retrieve, and an appropriate synchronization to enable that to happen safely, while also enabling appropriate notifications in both directions."

would be a good start for a description. I will update this issue when understanding more of the blog post and getting a better idea about what to put in the docs.

Start with the Channel API documentation page linked in the issue and compare its current content with the Channel API page. Add a description of what a channel does and a simple usage example, while documenting which framework versions apply; done means the page provides more than IntelliSense-level information.

Written by the indexing model from the issue text.