React Navigation needs a mention of useIonRouter

**URL**
https://ionicframework.com/docs/react/navigation

**What is missing or inaccurate about the content on this page?**
I've looked all over the docs, and I haven't been able to find a single mention of using `useIonRouter` within Ionic React.

I was trying to navigate to a page and specify the direction of the animation, and the only way I ended up finding `useIonRouter` was by following usage of the `RouterDirection` type.

Sure enough the import is [mentioned in `@ionic/vue`](https://ionicframework.com/docs/vue/utility-functions#router), but it doesn't exist for React.