Add DaC to Table of Contents

Author: eric-forte-elastic

README.md

@@ -16,6 +16,7 @@ This repository was first announced on Elastic's blog post, [Elastic Security op
   - [Overview of this repository](#overview-of-this-repository)
   - [Getting started](#getting-started)
   - [How to contribute](#how-to-contribute)
+  - [Detections as Code (DaC)](#detections-as-code-dac)
   - [Licensing](#licensing)
   - [Questions? Problems? Suggestions?](#questions-problems-suggestions)