Add "update screenshots" to release checklist (bevyengine#10369)

Author: cart

docs/release_checklist.md

@@ -12,6 +12,9 @@
 8. Bump version number for all crates, using the "Release" workflow.
 9. Create tag on GitHub.
 10. Bump `latest` tag to most recent release.
+11. Run this workflow to update screenshots:
+    * <https://github.com/bevyengine/bevy-website/actions/workflows/update-screenshots.yml>
+    * _This will block blog post releases (and take ~40 minutes) so do it early_.
 
 ## Release