docs: Fix runtime link in dev guide
The table of contents showed an incorrect link for building and
installing the runtime.
Fixes
* [Warning](#warning)
* [Assumptions](#assumptions)
-* [Build and install a Kata Containers runtime](#build-and-install-a-kata-containers-runtime)
+* [Build and install the Kata Containers runtime](#build-and-install-the-kata-containers-runtime)
* [Check hardware requirements](#check-hardware-requirements)
* [Enable full debug](#enable-full-debug)
* [Build and install Kata proxy](#build-and-install-kata-proxy)
