fix readme

[ljosberinn]

• incremental adoption under features has no explanation other than the code example
• standalone generation under features still refers to a --generated file which doesnt exist anymore
• consolidate examples. there are some in collapsibles and some at the bottom, wtf

[axelboc]

I feel like it would be worth having a more typical usage example near the top of the README. Perhaps something that disables/modifies a couple of core ESLint rules and a couple of React rules inside a custom override:

const dependencies = getDependencies();

const customReactOverride = createReactOverride({
  ...dependencies,
  rules: {
    /* some rule overrides */
  }
});

module.exports = createConfig({
  rules: {
    /* some rule overrides */
  },
  overrides: [customReactOverride],
});