Add Rspotify to the "Web API Libraries" page

[marioom]

I'm one of the maintainers of Rspotify, the most popular library for the Spotify API in the Rust programming language.

Back in July of 2020, when the spotify/web-api repo was still used for tickets like this one, I asked the devs to add Rspotify to the official page of Web API Libraries. It was this issue: https://github.com/spotify/web-api/issues/1595.

At that time, we were told that it'd be added the next time that list was updated. Unfortunately, more than a year has passed and it's still missing in there. Not that it has been a big problem anyway, because we were in the process of basically rewriting the entire library (more on that here: https://nullderef.com/blog/web-api-client/). But now that we've finally released the new version, I wanted to remind the Spotify devs to please include us in that page for those who try to get started with the Spotify API in the future.

Also, since a entire new section would be added for Rust, I would suggest to add aspotify as well, the second most popular library for the Spotify API.

Cheers,

Mario

[marioom]

Note that there's no need to add the `aspotify` crate anymore, since it seems to be archived now.