[Docs] Explain the different types of pointers and how to use them

[a62690705]

Where is the problem?

There is no explanation for pointer

What can we do better?

Explain the different types of pointers and how to use them

Anything else?

No response

[AzizAlqasem]

The following thread on X might be helpful for the documentation: https://x.com/Modular/status/1769823792527028471

The code can be found here: https://github.com/modularml/devrel-extras/blob/main/tweetorials/pointers/pointers.mojo