Add rp_hierarchy_code flag to README.rst.

Author: VStoilovskyi

README.rst

@@ -105,6 +105,7 @@ The following parameters are optional:
 - :code:`rp_hierarchy_dirs_level = 0` - Directory starting hierarchy level (from pytest.ini level) (default `0`)
 - :code:`rp_hierarchy_dirs = True` - Enables hierarchy for tests directories, default `False`. Doesn't support 'xdist' plugin.
 - :code:`rp_hierarchy_dir_path_separator` - Path separator to display directories in test hierarchy. In case of empty value current system path separator will be used (os.path.sep)
+- :code:`rp_hierarchy_code` - Enables hierarchy for parametrized tests, default `False`
 - :code:`rp_issue_system_url = https://bugzilla.some.com/show_bug.cgi?id={issue_id}` - issue URL (issue_id will be filled by parameter from pytest mark)
 - :code:`rp_issue_id_marks = True` - Enables adding marks for issue ids (e.g. "issue:123456")
 - :code:`rp_verify_ssl = True` - Verify SSL when connecting to the server