Cut down release note for image prefetching and add changelog entry

CHANGELOG.txt

@@ -6,6 +6,7 @@ Changelog
 
  * Phase out special-purpose panel types (`StreamFieldPanel`, `RichTextFieldPanel`, `ImageChooserPanel`, `DocumentChooserPanel`, `PageChooserPanel`, `SnippetChooserPanel`) in favour of `FieldPanel` (Matt Westcott)
  * Implement splitting of rich text blocks within StreamField (Jacob Topp-Mugglestone)
+ * Add support for image rendition prefetching (Andy Babic)
  * Upgrade ESLint and Stylelint configurations to latest shared Wagtail configs (Thibaud Colas, Paarth Agarwal)
  * Major updates to frontend tooling; move Node tooling from Gulp to Webpack, upgrade to Node v16 and npm v8, eslint v8, stylelint v14 and others (Thibaud Colas)
  * Change comment headers’ date formatting to use browser APIs instead of requiring a library (LB (Ben Johnston))

docs/releases/3.0.md

@@ -58,39 +58,7 @@ Trying to upload an image that's a duplicate of one already in the image library
 
 ### Image renditions can now be prefetched
 
-When using a queryset to render a list of items with images, you can now make use of Django's built-in ``prefetch_related()`` queryset method to prefetch the renditions needed for rendering with a single extra query. For long lists of items, or where multiple renditions are used for each item, this can provide a significant boost to performance.
-
-For example, say you were rendering a list of events (with thumbnail images for each). The queryset for your source data might look something like this:
-
-```python
-EventPage.objects.live().select_related("listing_image")
-```
-
-Now that renditions are prefetchable, you can reduce the number of additional database queries needed for rendering by updating the original queryset like so:
-
-```python
-EventPage.objects.live().select_related("listing_image").prefetch_related("listing_image__renditions")
-```
-
-If each image in your project has large numbers of renditions, you might want to consider using a ``Prefetch`` object to select only the renditions you need. For example:
-
-```python
-from django.db.models import Prefetch
-from wagtail.images import get_image_model
-
-
-# These are the renditions required for rendering
-renditions = get_image_model().get_rendition_model().objects.filter(
-    filter_spec__in=["fill-300x186", "fill-600x400", "fill-940x680"]
-)
-
-# `Prefetch` is used to only fetch the required renditions
-events = EventPage.objects.live().select_related("listing_image").prefetch_related(
-    Prefetch("listing_image__renditions", queryset=renditions)
-)
-```
-
-This feature was developed by Andy Babic.
+When using a queryset to render a list of items with images, you can now make use of Django's built-in ``prefetch_related()`` queryset method to prefetch the renditions needed for rendering with a single extra query. For long lists of items, or where multiple renditions are used for each item, this can provide a significant boost to performance. This feature was developed by Andy Babic.
 
 ### Other features