Add an async streams status quo for Barbara

[sophiajt]

This adds a status quo story for Barbara based on our experience using async streams in Nushell.

[rylev]

This is definitely a very interesting story - Thank you! It certainly has a bit of overlap with #48. I wonder what if we can reword the morals in light of #48 existing so we have a clear take-away from this story other than what is already covered in #48.

[sophiajt]

@rylev - Happy to, though I don't have a clear idea for what you have in mind.

#48 is talking about the details of writing async streams and where they are difficuilt. This is great information that I don't go over in this PR.

It doesn't seem to cover what I cover in this PR: namely that it's easy to go down the wrong path, to miss that streams are just iterators, and to miss that they can't be operated on in parallel. If you like, I can use that summary as the morals.

[nikomatsakis]

@jonathandturner that sounds helpful (using summary as morals)

[sophiajt]

Updated

[nikomatsakis]

Thanks @jonathandturner!

[rylev]

Awesome! I think this really highlights the issues of using streams where as the other stream story we have is about creating streams. Really great!