Change rls recommendation to rust-analyzer

[Absolucy]

rust-analyzer is typically more reliable than rls, has more features, and will eventually become Rust's official LSP implementation

Also, I added links to the plugins in the readme.

[kevinaboos]

Thanks for the PR, @aspenluxxxy! I will definitely look into this and probably change to using it over RLS. First I need to update our current Rustc nightly version to something more recent, since we're a little (ha) behind on that.

Once I do that, we'll experiment with newer plugins, such as this and also clippy.

[kevinaboos]

I experimented with Rust Analyzer, and while I do like it, it's not perfect. As such, I've decided to mention it as an alternative but not to remove the mention of RLS.

Recent changes to the README supersede the changes herein, thus I'm closing this as addressed by commit 168c14e.

Thanks again for the recommendation!