crates.io: an update to the malicious crate notification policy

The crates.io team has updated their policy on notifying users about malicious crates, opting not to publish a blog post for every detected case unless the crate has significant real-world usage or presents a security risk. They will continue publishing RustSec advisories for removed crates and provide updates via social media when necessary. Recent cases of malicious crates have been summarized, detailing actions taken against them and thanking relevant contributors.