docs: add caution about scripts processing when using head config

docs/src/content/docs/reference/configuration.mdx

@@ -444,6 +444,11 @@ starlight({
 });
 ```
 
+:::caution
+Scripts are placed into head using the `set:html` directive which is similar to using `is:inline` in that it [precludes these scripts from being processed by Astro](https://docs.astro.build/en/guides/client-side-scripts/#opting-out-of-processing).
+This means that if you want to include a local script and you need this to be processed, you'll probably need to [override or extend the Head component](/guides/overriding-components/#reuse-a-built-in-component).
+:::
+
 #### `HeadConfig`
 
 ```ts