Document omission of sparsefile in the packaging

debian/README.Debian

@@ -0,0 +1,7 @@
+sparsefile not included
+=======================
+
+Upstream provides a program `sparsefile` to create sparse files
+conveniently. It is not included in the Debian package. To create
+sparse files, use fallocate(1) provided by the essential package
+util-linux.