document document_dir function

[Zamiell]

Hello, and thanks for the library.

On Windows, the documents directory exists at the following location by default:

C:\Users\Alice\Documents

However, it is possible for the user to change this to any arbitrary directory by right clicking --> Properties --> Location.

I was curious if the document_dir function from this crate would work properly in such a scenario, so I went through the work of setting up a new VM to test it out.

Turns out it does work! But this was a pretty big time sink for me.
Can you document this fact in the docs so that others don't have to waste time in the same way?
Thank you.