QPR-12276 update read me

Author: pcaspers

Tools/PythonTools/Readme.md

@@ -22,6 +22,7 @@ Each object under a given key, `file_name`, has the following format (note that
           "optional_cols": [
             "col4"
           ]
+          "require_equal_optional_cols": false,
           "rename_cols": {
             "A": "a",
             "B": "b",
@@ -84,6 +85,7 @@ For `csv_settings`:
   - The `keys` specify which columns will be used as keys for the comparison. The comparison fails if all of these keys are not in both files to be compared.
   - The `use_cols` specifies on which columns the actual comparisons are evaluated.
   - The `optional_cols`, as with `use_cols` above, specifies columns on which comparisons are evaluated, but these columns are only included if they are present in both files. If they are not present in either file or if present in one file nad not the other, the corresponding comparison defined in `column_settings` below will not be evaluated for the missing column/s.
+  - The 'require_equal_optional_cols' specifies whether the test is failed if the optional columns are not all present in both files or not all absent in both files. It defaults to true if not given. In this case it is not allowed that an optional column is present in one file but not the other.
   - The `rename_cols` object specifies columns that should be renamed before the comparison is performed. In the example above, `A` would be renamed to `a` etc.
   - The `col_types` object allows you to explicitly specify the type of a given set of columns if necessary.
   - The `drop_rows` object allows you to specify a threshold for the values in a given set of columns. If the absolute value for a given row, in one of the specified columns, is below the threshold, the row is dropped from the comparison.