Add graphql-metrics to related projects list

Author: chrisbutcher

guides/related_projects.md

@@ -17,6 +17,7 @@ Want to add something? Please open a pull request [on GitHub](https://github.com
 - [`graphql-cache`](https://github.com/stackshareio/graphql-cache), a resolver-level caching solution
 - [`graphql-libgraphqlparser`](https://github.com/rmosolgo/graphql-libgraphqlparser-ruby), bindings to [libgraphqlparser](https://github.com/graphql/libgraphqlparser), a C-level parser.
 - [`graphql-docs`](https://github.com/gjtorikian/graphql-docs), a tool to automatically generate static HTML documentation from your GraphQL implementation
+- [`graphql-metrics`](https://github.com/Shopify/graphql-metrics), a plugin to extract fine-grain metrics of GraphQL queries received by your server
 - Rails Helpers:
   - [`graphql-activerecord`](https://github.com/goco-inc/graphql-activerecord)
   - [`graphql-rails-resolve`](https://github.com/colepatrickturner/graphql-rails-resolver)