Add more recent security release blog post

@estrike or @jritchey I added in a more up to date security release blog reference link that includes a more recent, small change where we removed the phrase "at least" in the section here:

GitLab releases patches for vulnerabilities in dedicated security releases. There are two types of security releases: a monthly, scheduled security release, released a week after the feature release (which deploys on the 22nd of each month), and ad-hoc security releases for critical vulnerabilities. You can see all of our regular and security release blog posts here. In addition, the issues detailing each vulnerability are made public on our issue tracker 30 days after the release in which they were patched.

We are dedicated to ensuring all aspects of GitLab that are exposed to customers or that host customer data are held to the highest security standards. As part of maintaining good security hygiene, it is highly recommended that all customers upgrade to at least the latest security release for their supported version. You can read more best practices in securing your GitLab instance in our blog post.

Can one of you please review and merge? thanks!