(usage): Output bug-reporting address.

src/ptx.c

@@ -1914,6 +1914,7 @@ Mandatory arguments to long options are mandatory for short options too.\n\
 \n\
 With no FILE or if FILE is -, read Standard Input.  `-F /' by default.\n\
 "), stdout);
+      printf (_("\nReport bugs to <%s>.\n"), PACKAGE_BUGREPORT);
     }
   exit (status);
 }