HBSD: improve the help options

- Fixes a tabulation problem.
- Adds an example for the '-t tmpdir' option.
Signed-off-by: Loic <loic.f@hardenedbsd.org>
MFC-to:		13-STABLE
MFC-to:		12-STABLE
(cherry picked from commit e1607958)

usr.sbin/hbsd-update/hbsd-update

@@ -130,9 +130,9 @@ usage() {
 	debug_print "\t-n\t\tDo not install kernel"
 	debug_print "\t-o\t\tDo not remove obsolete files/directories"
 	debug_print "\t-R\t\tUse system nameserver for the DNS-based version check"
-	debug_print "\t-r path\tBootstrap root directory <path>"
+	debug_print "\t-r path\t\tBootstrap root directory <path>"
 	debug_print "\t-s\t\tInstall sources (if present)"
-	debug_print "\t-t tmpdir\tTemporary directory"
+	debug_print "\t-t tmpdir\tTemporary directory (example: /root/tmp)"
 	debug_print "\t-U\t\tAllow unsigned updates"
 	debug_print "\t-v version\tUse a different version"
 	debug_print "\t-V\t\tVerbose output"