Change repository name to `dirs-next`

[NickHackman]

As mentioned on the Reddit post it makes sense to name the repository the same name as the crate, to avoid confusion and easier search-ability.

[tesuji]

There are disadvantages:

• It breaks links pointing back to this repository from crates.io and docs.rs .
• This repository is a cargo workspace with dirs-next crate at top-level directory. Workspace name dirs makes sense to me.

There are some alternative to avoid confusion and improve searching:

• Use github topics to tag dirs-next under repository description
• Move dirs-next crate to its own directories.

[nmccarty]

We've discussed this in our team meeting and feel that renaming the repository is not currently warranted.

We are open to revisiting this later if the name mismatch does turn out to cause friction.