Fix Buildah documentation error

In item #4 under https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html-single/building_running_and_managing_containers/index#proc_creating-images-from-scratch-with-buildah_assembly_building-container-images-with-buildah, the pasted code does not work unless the backslashes are removed.

I searched quite a while for causes of the errors I was seeing before I noticed that there were backslashes in the command.

Required change:

Either the command needs to be wrapped to a new line after each backslash or the backslashes need to be removed.