Update example of flatConfig to include typescript

Was having an issue for a few hours trying to get import/no-unresolved not picking up relative imports that don't include the extension like so:
```ts
import { add } from './utils';
```

After asking inside Discord, kkapp helped me by pointing out that I may need to configure the resolver to look for "ts" extensions. After adding it I went on a crusade to figure out how I had managed to miss that when migrating to flat configs.

The example given for non-flat configs tells you to include the typescript config, but the flatConfig variant does not, so for an out-of-the-box experience when migrating, it can cause a headache.

Author: intellix

README.md

@@ -205,7 +205,7 @@ export default tseslint.config(
   // other configs...
   {
     files: ['**/*.{ts,tsx}'],
-    extends: [importPlugin.flatConfigs.recommended],
+    extends: [importPlugin.flatConfigs.recommended, importPlugin.flatConfigs.typescript],
     // other configs...
   }
 );