Update Tcar-ug documentation manual.
    
     - Use =TCAR_WORKDIR= translation marker when the image path is
       defined. This is required in order for images to be loaded
       correctly. Remember that centos-art.sh script creates an instance
       of the main docbook file inside /tmp directory and produces it from
       it. Using absolute paths here we grantee the image will always be
       loaded. As we are using a translation marker, the repository
       working copy could be stored anywhere in the workstation.
    
     - Update graphic design of monolithic.svgz file.