Add --dispvm to qvm-run documentation

doc/vm-tools/qvm-run.rst

@@ -14,6 +14,8 @@ SYNOPSIS
 
 OPTIONS
 =======
+--dispvm
+  Pass this option instead of vmname to start new DisposableVM
 
 AUTHORS
 =======

qubes-rpc/qvm-run

@@ -22,6 +22,7 @@
 
 if [ $# -lt 2 ] ; then 
 	echo "Usage: $0 vmname command arguments"
+	echo "  you can use \$dispvm or --dispvm instead of vmname to start new DisposableVM"
 	exit 1
 fi
 VMNAME=$1