[Feature]: add example with usage of both keyof & typeof operators

[reznikovAndrey]

Description

I think it's necessary to provide example with usage of both keyof & typeof operators.
The final solution like this will be more clear.

Explanation

In my opinion, after completing challenge with usage of keyof operator newcomer might think, that provided examples are only valid way of using keyof.

In other words:

1. You create new type with typeof.
2. You need use keyof with this type.

But in real world there are a lot of examples of using both keyof & typeof operators together.
I consider this as best practice.

[bautistaaa]

these are meant to be taken in order when you enroll in the foundations track. typeof is a challenge before you encounter keyof. perhaps we should remove these from the explore page and point them to the track

[bautistaaa]

i also don’t understand the best practice part of your comment. the pref would usually be typeof standalone so you can reuse the type and making a separate type if you needed the union

of course this is situational

[reznikovAndrey]

Yeah, you are right, that's situational.
My fault, it's not best practice.

At least may be it would be better to have explicit example of usage of this operators together?