docs: generate the listing images instead of committing them

The five PNGs are generated output, like the build ZIP, so they leave
git and docs/amo/screenshots/ is ignored. The README's command produces
them, and with squash merges they never reach develop or main, so the
repository needs no Git LFS.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/amo/README.md

@@ -60,6 +60,11 @@ prints the ZIP's path.
 Upload in this order, with these captions. Each image is 1280×800, the size AMO
 recommends, and carries no added text, as Mozilla's listing guide advises.
 
+The images are not committed. Generate them as described under
+[Regenerating the images](#regenerating-the-images); they land in
+`docs/amo/screenshots/`, which git ignores, so the links below work once you
+have.
+
 | Image | Caption |
 |---|---|
 | [1-address-bar.png](screenshots/1-address-bar.png) | Type gpt and your question in the address bar. ChatGPT opens with it filled in. |
@@ -75,9 +80,10 @@ Suggested caption: "Every setting on one simple page."
 ## Regenerating the images
 
 The images are the options page's drawings, enlarged by
-[`screenshots.html`](screenshots.html), which reuses `options/options.css`. When
-a drawing in `options/options.html` changes, copy the change into
-`screenshots.html`, then run these from the repository root:
+[`screenshots.html`](screenshots.html), which reuses `options/options.css`. They
+are generated rather than committed, like the build ZIP. When a drawing in
+`options/options.html` changes, copy the change into `screenshots.html`. Then,
+to produce the images, run these from the repository root:
 
 ```sh
 python3 -m http.server 8766 --bind 127.0.0.1 &