Outdated instructions on how to start graphql-language-service-server

[Server readme](https://github.com/graphql/graphiql/blob/2de91ba08920927624ec6f6c8d86b6abc46b6d26/packages/graphql-language-service-server/README.md) includes note about using `graphql` "binary" to start it:

> The library includes a node executable file which you can find in ./node_modules/.bin/graphql.js after installation.

But that binary is deprecated and refers user to `graphql-language-service-cli` instead. [Here is the source of the script](https://github.com/graphql/graphiql/blob/2de91ba08920927624ec6f6c8d86b6abc46b6d26/packages/graphql-language-service/src/temp-bin.ts).

So it's the [graphql-language-service-cli script](https://github.com/graphql/graphiql/blob/2de91ba08920927624ec6f6c8d86b6abc46b6d26/packages/graphql-language-service-cli/bin/graphql.js) that can be used to start the server now. Also, the `cli` includes the server as dependency so no need to install server dependency separately.

I think this all should be clarified in the server's readme. It could just say that to start the server in standalone mode, one should use `graphql-language-service-cli` instead.