virsh: Fix man page argument ordering for vol-delete command

The proper command order is 'virsh vol-delete volume pool'. While
making the modification clean up the description a bit too in order
to help clarify under what circumstances the volume could be found
if the pool name was not provided.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>

tools/virsh.pod

@@ -4057,13 +4057,18 @@ When I<--reflink> is specified, perform a COW lightweight copy,
 where the data blocks are copied only when modified.
 If this is not possible, the copy fails.
 
-=item B<vol-delete> [I<--pool> I<pool-or-uuid>] I<vol-name-or-key-or-path>
+=item B<vol-delete> I<vol-name-or-key-or-path> [I<--pool> I<pool-or-uuid>]
 [I<--delete-snapshots>]
 
 Delete a given volume.
-I<--pool> I<pool-or-uuid> is the name or UUID of the storage pool the volume
-is in.
-I<vol-name-or-key-or-path> is the name or key or path of the volume to delete.
+
+I<vol-name-or-key-or-path> is the volume name or key or path of the volume
+to delete.
+
+[I<--pool> I<pool-or-uuid>] is the name or UUID of the storage pool the volume
+is in. If the volume name is provided instead of the key or path, then
+providing the pool is necessary to find the volume to be deleted; otherwise,
+the first volume found by the key or path will be used.
 
 The I<--delete-snapshots> flag specifies that any snapshots associated with
 the storage volume should be deleted as well. Not all storage drivers