Add import to example in README

Author: jdolle

packages/libraries/federation-link-utils/README.md

@@ -35,6 +35,7 @@ type User {
 
 ```typescript
 // specs.ts
+import { detectLinkedImplementations, LinkableSpec } from '@graphql-hive/federation-link-utils'
 
 const exampleSpec = new LinkableSpec('https://specs.graphql-hive.com/example', {
   'v0.1': resolveImportName => (typeDefs: DocumentNode) => {