Docs: type definitions with apollo gql template literal

[aichbauer]

Right now we define our types with JavaScript and I do not plan on changing this in this project since, I like writing everything in the same language. But with gql template literals we have also a way to create our types. It is not a way I really like, but since it is possible with this project and very popular to create your types this way we should definitively document this way, also because it is very easy to switch.

Instead of:

const UserType = new GraphQLObjectType({
  name: 'User',
  description: 'This represents a User',
  fields: () => ({
    id: {
      type: GraphQLInt,
      resolve: (user) => user.id,
    },
  }),
});

you can write something similar to:

const typeDefs = gql`
  type UserType {
    "This represents a User"
    id: Int
  }
`;

const resolvers = {
  UserType: {
    id: (user) => user.id
  }
};