Add some basic streaming engine documentation

[wence-]

Description

This is a start, but still incomplete because the installation of various dependencies is tricky. But better than nothing.

Checklist

• [x] I am familiar with the Contributing Guidelines.
• [x] New or existing tests cover these changes.
• [x] The documentation is up to date with these changes.

[TomAugspurger]

fa18b9b should have all the suggestions (lightly adapted).

[btepera]

Thanks, this looks good to me!

[vyasr]

Does @wence- have time to finish this or do we want someone else to take over and get this past the finish line? I think the remaining changes are all pretty minor ones.

[wence-]

Does @wence- have time to finish this or do we want someone else to take over and get this past the finish line? I think the remaining changes are all pretty minor ones.

I think everything is addressed now.

[wence-]

/merge