So #bevy has so many wonderful examples, but when you're looking for something simple in rendering, all of the examples tend to look way more complex than what you need. So I decide "naw, none of these are it", so I went and read a bunch of code & examples and wrote my own:
Then some of the rendering people in the discord directed me to the post-processing example, and after understanding things I saw it was what I needed. Learning is great! (and updated my gist)