Improve clarity of Pages > Build Image > Limitations

The Pages > Build Image > Limitations section lists a set of features, referring to them as "limitations" without explicitly stating what is limited about them (implicitly: the limitation is that these features are unsupported). This PR updates the section to state this intent explicitly.

Author: 1000hz

src/content/docs/pages/configuration/build-image.mdx

@@ -79,7 +79,7 @@ If you were previously relying on the default versions of any languages or tools
 
 ### Limitations
 
-Here are some limitations with the v2 build system:
+The following features are currently not supported when using the v2 build system:
 
 - Specifying Node.js versions as codenames (for example, `hydrogen` or `lts/hydrogen`).
 - Detecting Yarn version from `yarn.lock` file version.