virt-install, virt-sparsify: add page (#4333)

pages/common/virt-sparsify.md

@@ -0,0 +1,13 @@
+# virt-sparsify
+
+> Make virtual machine drive images thin-provisioned.
+> NOTE: Use only for offline machines to avoid data corruption.
+> Home page: <https://libguestfs.org/>.
+
+- Create a sparsified compressed image without snapshots from an unsparsified one:
+
+`virt-sparsify --compress {{path/to/image.qcow2}} {{path/to/image_new.qcow2}}`
+
+- Sparsify an image in-place:
+
+`virt-sparsify --in-place {{path/to/image.img}}`