Merge branch 'patch-1' into 'master'

Update security.md

See merge request !119

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.
+for the timeline of handling a critical security release.
+Only a subset of the security releases are critical.
 # Security Releases