Update the ApolloServer resolvers argument documentation

[mdawar]

Updated the documentation of the resolvers argument of the ApolloServer constructor and the makeExecutableSchema function, added a note that the resolvers argument may be a single resolver map or an array of resolver maps with an example.

const authorResolvers = {
  Query: {
    authors() {
      return authors;
    }
  },
};

const bookResolvers = {
  Query: {
    books() {
      return books;
    }
  },
};

new ApolloServer({
  typeDefs,
  // The resolver map objects are deeply merged
  resolvers: [authorResolvers, bookResolvers],
});

[apollo-cla]

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[StephenBarlow]

Thanks for the PR @mdawar! This API reference received an overhaul recently, and the array option for this argument is now reflected: https://www.apollographql.com/docs/apollo-server/api/apollo-server/#resolvers