[docs] difference in schema registration example<->README

[haf]

Examples does:

import schema from '../../../schema.json';
// snip
  beforeEach(() => {
// snip
    cy.mockGraphql({ schema });

Docs do:

  cy.task("getSchema").then(schema => {
    cy.mockGraphql({
      schema,
      operations: { ... }
    });
  });

There's also a code-generator in the example and a command to update the schema json file. It's unclear:

• whether to use https://github.com/apollographql/apollo-tooling or the https://graphql-code-generator.com/ in your example for generation
  • what to do if the API already is typed from the server, in e.g. TypeScript
• how to manage the schema.json file; commit? And why can't cypress take it by just calling the API that it's testing? https://stackoverflow.com/questions/37397886/get-graphql-whole-schema-query