xz: Make the man page more friendly to doclifter.

Thanks to Eric S. Raymond.
diff --git a/src/xz/xz.1 b/src/xz/xz.1
index 696a2f4..e64d36a 100644
--- a/src/xz/xz.1
+++ b/src/xz/xz.1
@@ -12,9 +12,10 @@
 .
 .SH SYNOPSIS
 .B xz
-.RI [ option ]...
-.RI [ file ]...
-.PP
+.RI [ option... ]
+.RI [ file... ]
+.
+.SH COMMAND ALIASES
 .B unxz
 is equivalent to
 .BR "xz \-\-decompress" .