diff --git a/img.mu b/img.mu
index deca2a29..318c06e3 100644
--- a/img.mu
+++ b/img.mu
@@ -1,4 +1,16 @@
 # load an image from disk and display it on screen
+#
+# To build:
+#   $ ./translate shell/*.mu                        # generates code.img
+# Load a pbm, pgm or ppm image (no more than 255 levels)
+#   $ dd if=/dev/zero of=data.img count=20160
+#   $ cat x.pbm |dd of=data.img conv=notrunc
+# or
+#   $ cat t.pgm |dd of=data.img conv=notrunc
+# or
+#   $ cat snail.ppm |dd of=data.img conv=notrunc
+# To run:
+#   $ qemu-system-i386 -hda code.img -hdb data.img
 
 type image {
   type: int  # supported types: