Sunsetting self-assessments subproject

[Tabitha Sable]

SIG Security Friends,

We're writing to let you know that we are archiving the Security Self-Assessments subproject, which was formerly led by Ala Dewberry.

Thank you so much, Ala, for leading Self-Assessments with skill, warmth, and curiosity. You helped so many contributors learn about the security of their own projects and empower themselves via your workshops, documentation, and facilitation of self-assessment processes. We're so glad to have gotten to work with you and help out sometimes!

Thank you, Pushkar Joglekar, for leading the first self-assessment, starting the
 subproject, and mentoring Ala into this leadership role!

The documentation and artifacts from the subproject will remain available under https://github.com/kubernetes/sig-security/ for future reference.

With love,
Cailyn, Ian, and Tabitha