Merge branch 'improve-security-cross-link' into 'master'

Properly cross-link security.md

See merge request !115

doc/security.md

+Also see [the GitLab Handbook on the Critical Release Process](https://about.gitlab.com/handbook/engineering/critical-release-process/)
+for the overall timeline of handling a security release.
+
 # Security Releases
 Security vulnerabilities in GitLab and its dependencies are to be addressed with
@@ -58,9 +61,6 @@ disclose them.
 Be sure NOT to pre-announce which GitLab versions are affected, since that may
 allow malicious users to narrow the search space.
-See [https://about.gitlab.com/handbook/engineering/critical-release-process/] for
-more details on how to handle a critical security release.
-
 ## Process
 ### Before the release