update doc

README.md

@@ -17,5 +17,9 @@ It expects that the json input is formatted as an object containing an array of
 
 ## Advanced configuration
 
-Advanced settings can be provided via a top level json key named "config". Below are options that can be set via this config key:
+Advanced settings can be provided via a top level json key named "config". Here is a table of options that can be set via this config key.
-- key-order
+| Key     | Example Value | Description               |
+|---------------|---------------|---------------------------|
+| key-order | "Column3,Column1,Column2"| Comma separated list of column names in the desired order |
+| overwrite-file | true | Boolean indicating whether output file should be overwritten if it already exists |
+-