docs: Fix debian docker link
Fixed the Debian install guide which was pointing to the Ubuntu Docker
install guide by mistake.
3. Decide which container manager to use and select the corresponding link that follows:
- - [Docker](docker/ubuntu-docker-install.md)
+ - [Docker](docker/debian-docker-install.md)
- [Kubernetes](https://github.com/kata-containers/documentation/blob/master/Developer-Guide.md#run-kata-containers-with-kubernetes)
