(usage): Tell where to report bugs.

src/expr.c

@@ -144,6 +144,7 @@ Comparisons are arithmetic if both ARGs are numbers, else lexicographical.\n\
 Pattern matches return the string matched between \\( and \\) or null; if\n\
 \\( and \\) are not used, they return the number of characters matched or 0.\n\
 "));
+      puts (_("\nReport bugs to bug-gnu-utils@gnu.ai.mit.edu"));
     }
   exit (status);
 }