apollo-server-express: mention graphql-js in README

See #4949. This matches what we do in the docs site.

I have not done an exhaustive search across READMEs for more problems like this; PRs welcome.

packages/apollo-server-express/README.md

@@ -5,7 +5,7 @@
 This is the Express and Connect integration of GraphQL Server. Apollo Server is a community-maintained open-source GraphQL server that works with many Node.js HTTP server frameworks. [Read the docs](https://www.apollographql.com/docs/apollo-server/). [Read the CHANGELOG.](https://github.com/apollographql/apollo-server/blob/main/CHANGELOG.md)
 
 ```shell
-npm install apollo-server-express
+npm install apollo-server-express graphql
 ```
 
 ## Express