Mention tool virt-sparsify

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>

Author: netoptimizer

setup-testlab/create_vm_image.org

@@ -114,7 +114,8 @@ End-result: A virtual machine with:
 This Fedora-Cloud image have a 10 sec. delay when logging in as root, remove
 that via editing /root/.ssh/authorized_keys.
 
-* Increasing disk capacity
+* Disk capacity
+** Increasing VM disk capacity
 
 The remaining disc capacity is getting low, it will be unfortunate if this
 disrupt the tutorial. Thus, we resize the VM disk. First shutdown the VM.
@@ -135,6 +136,11 @@ partprobe
 resize2fs /dev/vda1
 #+end_example
 
+** Reduce VM image size
+
+Before uploading, use the tool =virt-sparsify= to reduce disk capacity used
+by VM image. And afterwards also compress image, to reduce download size.
+
 * Extra manual changes
 
 Cloned some git trees in user 'fedora' home directory.