Add a security txt https://securitytxt.org/

ac2629c7 · Sid Sijbrandij · 0aca6d56 · ac2629c7
--- a/security.txt
+++ b/security.txt
+Contact: security@gitlab.com
+Acknowledgments: https://about.gitlab.com/security/vulnerability-acknowledgements/
+Preferred-Languages: en
+Canonical: https://about.gitlab.com/security/disclosure/
+Policy: https://hackerone.com/gitlab
+Hiring: https://about.gitlab.com/jobs/