Mention sendbug(1) as a means of reporting bugs

src/etc/motd

@@ -2,3 +2,11 @@ OpenBSD ?.? (UNKNOWN)
 
 Welcome to OpenBSD.
 
+Please use the sendbug(1) utility to report bugs in the system.
+Before reporting a bug, please try to reproduce it with the
+latest version of the code.
+
+With bug reports, please try to ensure that enough information
+to reproduce the problem is enclosed, and if a known fix for it
+exists, include that as well.
+