docs: Add TOC
Added a Table of Contents to the top-level README.
# Documentation
+* [Getting Started](#getting-started)
+* [More User Guides](#more-user-guides)
+* [Kata Use-Cases](#kata-use-cases)
+* [Developer Guide](#developer-guide)
+ * [Design and Implementations](#design-and-implementations)
+ * [How to Contribute](#how-to-contribute)
+ * [Code Licensing](#code-licensing)
+ * [The Release Process](#the-release-process)
+* [Help Improving the Documents](#help-improving-the-documents)
+
The [Kata Containers](https://github.com/kata-containers)
documentation repository hosts overall system documentation, with information
common to multiple components.
