Update the example in the docs to use a more "realistic" example

[tomanagle]

Just had a bit of confusion with the key, where it wasn't clear that it needs to be dynamic and was treated more like a namespace. It's probably not common but if someone does this it could lead to some really unexpected results.

For example, we want to cache a resource called user and the key was set to user instead of user_${userId}.

I'm happy to update the docs to either switch out the PI example or add another example.

Great library btw, going to keep us out of trouble :)

[Xiphe]

Hey @tomanagle you're right! that's a great idea!
I was also thinking about using tables like here to better describe what's happening.

If you'd like I'll happily accept a PR for this 👍