Fix codegen script

[bennypowers]

Prevent

Unable to find any GraphQL type definitions for the following pointers:

> wc-registry@0.0.0 build:graphql
> graphql-codegen

  ✔ Parse configuration
  ❯ Generate outputs
    ❯ Generate src/schema.ts
      ✔ Load GraphQL schemas
      ✖ Load GraphQL documents
        →           - src/**/*.subscription.graphql
        Generate


 Found 1 error

  ✖ src/schema.ts
    Error:
          Unable to find any GraphQL type definitions for the following pointers:

              - src/**/*.fragment.graphql
              ,
              - src/**/*.mutation.graphql
              ,
              - src/**/*.query.graphql
              ,
              - src/**/*.subscription.graphql

        at prepareResult (/Users/bennyp/Developer/wc-catalog/packages/wc-registry/node_modules/@graphql-tools/load/index.cjs.js:591:15)
        at loadTypedefs (/Users/bennyp/Developer/wc-catalog/packages/wc-registry/node_modules/@graphql-tools/load/index.cjs.js:556:12)
        at processTicksAndRejections (node:internal/process/task_queues:94:5)
        at async CodegenContext.loadDocuments (/Users/bennyp/Developer/wc-catalog/packages/wc-registry/node_modules/@graphql-codegen/cli/bin.js:737:31)
        at async /Users/bennyp/Developer/wc-catalog/packages/wc-registry/node_modules/@graphql-codegen/cli/bin.js:916:55
        at async Task.task (/Users/bennyp/Developer/wc-catalog/packages/wc-registry/node_modules/@graphql-codegen/cli/bin.js:760:17)
    Error:
          Unable to find any GraphQL type definitions for the following pointers:

              - src/**/*.fragment.graphql
              ,
              - src/**/*.mutation.graphql
              ,
              - src/**/*.query.graphql
              ,
              - src/**/*.subscription.graphql

        at prepareResult (/Users/bennyp/Developer/wc-catalog/packages/wc-registry/node_modules/@graphql-tools/load/index.cjs.js:591:15)
        at loadTypedefs (/Users/bennyp/Developer/wc-catalog/packages/wc-registry/node_modules/@graphql-tools/load/index.cjs.js:556:12)
        at processTicksAndRejections (node:internal/process/task_queues:94:5)
        at async CodegenContext.loadDocuments (/Users/bennyp/Developer/wc-catalog/packages/wc-registry/node_modules/@graphql-codegen/cli/bin.js:737:31)
        at async /Users/bennyp/Developer/wc-catalog/packages/wc-registry/node_modules/@graphql-codegen/cli/bin.js:916:55
        at async Task.task (/Users/bennyp/Developer/wc-catalog/packages/wc-registry/node_modules/@graphql-codegen/cli/bin.js:760:17)

Also add quick start to readme