Add link to GraphiQL in Object Types Tutorial (#1695)

* Adding link to GraphiQL in Object Types tutorial

* Update src/pages/graphql-js/object-types.mdx

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Co-authored-by: Benjie <[email protected]>

Author: adamosimpson21

src/pages/graphql-js/object-types.mdx

@@ -135,7 +135,7 @@ When you issue a GraphQL query against an API that returns object types, you can
 }
 ```
 
-If you run this code with `node server.js` and browse to http://localhost:4000/graphql you can try out these APIs with GraphiQL.
+If you run this code with `node server.js` and browse to http://localhost:4000/graphql you can try out these APIs with [GraphiQL](https://github.com/graphql/graphiql).
 
 This way of defining object types often provides advantages over a traditional REST API. Instead of doing one API request to get basic information about an object, and then multiple subsequent API requests to find out more information about that object, you can get all of that information in one API request. That saves bandwidth, makes your app run faster, and simplifies your client-side logic.