docs: add info for how @meta directive works (#6648)

Author: jdolle

packages/web/docs/src/content/specs/link-specifications.mdx

@@ -83,5 +83,15 @@ import explorerMetadataFilterImage from '../../../public/docs/pages/specs/link-s
   className="mt-10 max-w-2xl rounded-lg drop-shadow-md"
 />
 
+#### Usage
+
+`@meta` can be applied to schemas, types, interfaces, and fields. A field's metadata is a union of
+all applied metadata. This is applied using the following rules:
+
+1. meta on a schema applies to every field in the schema.
+2. meta on a type applies to every field in that exact type.
+3. meta on an interface applies to every field in that interface on every implemented type.
+4. meta on a field applies only to that field for that type.
+
 </Tabs.Tab>
 </Tabs>