text: Title: build/README.md suggests using outdated docker-machine
  Body: <!-- Please only use this template for submitting enhancement requests -->
  
  **What would you like to be added**:
  
  The Docker Machine project is currently in maintenance mode (https://github.com/docker/machine/issues/4537) and there are different ways to utilize remote hosts for Docker containers to build Kubernetes. I believe the **build/README.md** documentation should be updated to reflect this.
  
  **Why is this needed**:
  
  Docker Machine is in maintenance mode and on the Docker website, it's listed as superseded. Kubernetes docs should recommend a better method before Docker Machine fades into non-maintenance.
  