Update readme with new capability

plugins/image-prioritizer/readme.txt

@@ -7,7 +7,7 @@ License:      GPLv2 or later
 License URI:  https://www.gnu.org/licenses/gpl-2.0.html
 Tags:         performance, optimization, image, lcp, lazy-load
 
-Prioritizes the loading of images and videos based on how visible they are to actual visitors; adds fetchpriority and applies lazy loading.
+Prioritizes the loading of images and videos based on how they appear to actual visitors: adds fetchpriority, preloads, lazy-loads, and sets sizes.
 
 == Description ==
 
@@ -27,7 +27,9 @@ The current optimizations include:
    1. Apply lazy loading to `IMG` tags based on whether they appear in any breakpoint’s initial viewport.
    2. Implement lazy loading of CSS background images added via inline `style` attributes.
    3. Lazy-load `VIDEO` tags by setting the appropriate attributes based on whether they appear in the initial viewport. If a `VIDEO` is the LCP element, it gets `preload=auto`; if it is in an initial viewport, the `preload=metadata` default is left; if it is not in an initial viewport, it gets `preload=none`. Lazy-loaded videos also get initial `preload`, `autoplay`, and `poster` attributes restored when the `VIDEO` is going to enter the viewport.
-5. Ensure that [`sizes=auto`](https://make.wordpress.org/core/2024/10/18/auto-sizes-for-lazy-loaded-images-in-wordpress-6-7/) is added to all lazy-loaded `IMG` elements.
+5. Responsive image sizes:
+   1. Ensure [`sizes=auto`](https://make.wordpress.org/core/2024/10/18/auto-sizes-for-lazy-loaded-images-in-wordpress-6-7/) is added to all lazy-loaded `IMG` elements.
+   2. Compute the `sizes` attribute using the widths of an image collected from URL Metrics for each breakpoint (when not lazy-loaded since then handled by `sizes=auto`).
 6. Reduce the size of the `poster` image of a `VIDEO` from full size to the size appropriate for the maximum width of the video (on desktop).
 
 **This plugin requires the [Optimization Detective](https://wordpress.org/plugins/optimization-detective/) plugin as a dependency.** Please refer to that plugin for additional background on how this plugin works as well as additional developer options.