Add doc for resultMemoize(projectorFn, isEqual) and createSelectorFactory()

Please add this example to the docs: https://www.youtube.com/watch?v=E7GKnjGCXzU&t=641s&ab_channel=NgTalks

Also upvoted by 11 people in this issue: https://github.com/ngrx/platform/issues/724

I would be willing to submit a PR for the docs :heart:

[ ] Yes (Assistance is provided if you need help submitting a pull request) [x] No