Moving docs from /vX to /docs; we will use branches for old versions.

docs/user-guide/security-context.md

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+A security context defines the operating system security settings (uid, gid, capabilities, SELinux role, etc..) applied to a container. See [security context design](https://github.com/kubernetes/kubernetes/blob/{{page.githubbranch}}/docs/design/security_context.md) for more details.