updated groupBy in docs

features/tabular-statistics-tool/README.md

@@ -20,7 +20,8 @@ This plugin computes statistical measures on numeric and floating point data col
 ## Usage:
 - A directory containing one or more tabular files in the supported formats
 - Each file must include numeric and floating point data columns
-- If a `groupBy` column is specified in the input arguments, it must be present in the data
+- Ensure that the `groupBy` variables are included in the file pattern
+
 
 For more information on WIPP, visit the [official WIPP page](https://isg.nist.gov/deepzoomweb/software/wipp).