feat: svg rasterization upgrade guide

src/content/docs/en/guides/upgrade-to/v6.mdx

@@ -164,6 +164,24 @@ import { z } from 'astro/zod';
 
 <ReadMore>See more about [the `astro/zod` module](/en/reference/modules/astro-zod/).</ReadMore>
 
+### SVG rasterization
+
+Astro's default Sharp image service now supports converting SVG files to raster files (such as PNG, WebP, etc.). Note that this is subject to many limitations, for instance SVGs with embedded fonts might not be converted properly.
+
+#### What should I do?
+
+If you were previously relying on code like this to automatically skip SVGs:
+
+```astro
+<Image src={imageThatMightBeAnSvg} format="avif" alt="example" />
+```
+
+You'll now need to check the format beforehand to avoid converting SVGs to raster images:
+
+```astro
+<Image src={imageThatMightBeAnSvg} format={imageThatMightBeAnSvg.src.format === "svg" ? "svg" : "avif"} alt="example" />
+```
+
 ### Official Astro integrations
 
 All of [Astro's official server adapters](/en/guides/on-demand-rendering/#server-adapters) have also updated to a new major version to accompany the upgrade to Vite v7.0 with Vite's Environment API as the development server and production bundler.