--- a/readme.rst	Fri Nov 10 09:39:12 2017 +0200
+++ b/readme.rst	Fri Nov 10 10:20:03 2017 +0200
@@ -51,6 +51,10 @@
       -p PRESSURE, --pressure PRESSURE
                             The pressure (in hPa) at lidar level, required if
                             using US Standard atmosphere
+      -D DARK_FILES, --dark_files DARK_FILES
+                            Location of files containing dark measurements.
+                            Use relative path and filename wildcars, see 'files'
+                            parameter for example.
       -d, --debug           Print dubuging information.
       -s, --silent          Show only warning and error messages.
       --version             Show current version.