Created GH-16147 for replacing the *from_what* argument with *whence* in the IO tutorial. 

I would like to consider following up on this with another PR that adds the IO constants `SEEK_SET`, `SEEK_CUR`, and `SEEK_END` to the tutorial. Those constants would be particularly useful for new users of the language, and would likely make the tutorial easier to understand for those who don't have prior experience with using `seek()`.

However, I figured that replacing *from_what* with *whence* would be significantly less controversial and easier to review, which is why they will be in separate PRs.