I'd recommend against an overview. Short stories are short, and figuring out what they are and what they're doing is often a lot of the story's bulk. You want them coming in like a real reader would -- not knowing almost anything except what magazine or anthology they're reading.
General Genre/Subgenre. This is often a quick way for potential readers to gauge interest -- some readers can't stand Hard SF; others love a good fairy tale retelling; etc. etc. This helps you find the readers that are right for your story.
Similarly, keywords. Knowing the story has a trans protagonist, or mermaids in it, or astronauts, can help grab potential beta readers -- or keep away the ones who just don't like stories with that particular element. (P.S. Somebody please write a story about a trans mermaid astronaut, thanks)
Where you're at; what you're after. Tell the readers what you want from feedback. A lot of readers don't really know to focus -- and this can change depending on the author and the story. Do you prefer criticism be exhaustively explained, or are you just looking for quick pointers? Should readers indicate issues that would take a complete rewrite to fix, or assume the story's core is fairly well-set? Is this your first time getting feedback on your work, or your fifteenth? Will curt comments depress you; will overenthusiastic comments make you skeptical?
You definitely don't need to answer all these -- but do give some thought yourself to what kind of feedback you'd like, and what you've appreciated in feedback you've seen (or, what you'd rather avoid). Give the reader some points about how to write effectively for you.
Previous credits mostly work to your benefit if you've published things elsewhere, or are active in a particular community; etc. etc. It can be a way to signal, "Look, I'm serious about this," or "Look, I'm not some rando; I've had stories published in $MAGAZINE!
Questions you'd like answered. If you have specific worries or doubts you'd like readers to weigh in on, provide them upfront -- just make sure it doesn't wind up as an easily-avoidable spoiler.
That's pretty much it. Most readers pick a story up with little-to-no prep -- you probably want to preserve that as much as possible, which means you don't want to prep your beta readers too much either!