more usage info
diff --git a/progs/trivial/flat-clip.c b/progs/trivial/flat-clip.c
index 3e073ac..dbe17a3 100644
--- a/progs/trivial/flat-clip.c
+++ b/progs/trivial/flat-clip.c
@@ -129,6 +129,8 @@
    printf("  z/Z:  change triangle size\n");
    printf("  r/R:  rotate\n");
    printf("  p:    toggle line/fill mode\n");
+   printf("  s:    toggle smooth/flat shading\n");
+   printf("  f:    switch polygon fill mode\n");
 }