ps: document -T option

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/include/usage.h b/include/usage.h
index 6f9d155..c7013de 100644
--- a/include/usage.h
+++ b/include/usage.h
@@ -3424,6 +3424,9 @@
        "Report process status\n" \
      "\nOptions:" \
      "\n	-o col1,col2=header	Select columns for display" \
+	IF_FEATURE_SHOW_THREADS( \
+     "\n	-T			Show threads" \
+	)
 
 #else /* !ENABLE_DESKTOP */