Should document the getter overloads of `.config()` method

Nobody has claimed this yet.

Right now, there's no official, documented, way to read an instance's `name` or `storeName` properties. Having access to those can be useful for debugging.

They *are* technically accessible through the `localforage._config` property. However, that isn't documented, and the underscore conventionally means that users should avoid accessing it.

A basic example where this would be useful:
```js
const results = await store.getItems();
console.log("loaded items from", store._config.storeName);
```

Locate the documented `.config()` API and review its getter overloads. Document how to read an instance's `name` and `storeName` properties through the supported API, and include enough guidance that users do not need to access the underscored `_config` property.

Written by the indexing model from the issue text.