monsoon: Add note of output column format in help string.

Change-Id: I85440a4e539a1b1cf1683b0b4a7837998dd5df70
diff --git a/tools/utils/monsoon.py b/tools/utils/monsoon.py
index a179bca..d13cf3a 100755
--- a/tools/utils/monsoon.py
+++ b/tools/utils/monsoon.py
@@ -33,6 +33,15 @@
 
   Get unlimited 200Hz data from device attached at /dev/ttyACM0
   python monsoon.py --samples -1 --hz 200 --device /dev/ttyACM0
+
+Output columns for collection with --samples, separated by space:
+
+  TIMESTAMP OUTPUT OUTPUT_AVG USB USB_AVG
+   |                |          |   |
+   |                |          |   ` (if --includeusb and --avg)
+   |                |          ` (if --includeusb)
+   |                ` (if --avg)
+   ` (if --timestamp)
 """
 
 import fcntl