Improve docs to add "graphql-tools" better examples

[wenderjean]

Hey guys,

Do you think it worths adding more examples on README regarding the integration with graphql-tools? It took some time to me to understand how to add my custom scalars on mockGraphql, even though it is pretty straightforward I had to took a look at the source to have a clear understanding on it. :)

[jfairley]

@wenderjean I'm trying to figure that out myself. Care to point me to how to define a custom scalar?

[jfairley]

I ended up making something like this: #17 (comment)

I created a Date scalar in my backend which is a without-time date (like "2020-12-07").

Added this to my test. Not exactly sure if it's the "right" thing, but it works for my case.

    cy.mockGraphql({
      ...
      mocks: {
        Date(obj, args, context, field) {
          if (obj[field.fieldName]) return obj[field.fieldName];
          if (field.variableValues[field.fieldName]) return field.variableValues[field.fieldName];
          return "2020-11-11";
        },
      },
    })