Describe what this module does

From readme file it looks like it does not provide any services or api but add phpoffice spreadsheet libarary to the main composer.json base file.
Any additional documentation will need to be followed from https://github.com/PHPOffice/PhpSpreadsheet or from its docs https://phpspreadsheet.readthedocs.io/en/latest/

Additionally, can have a look into https://www.drupal.org/forum/support/module-development-and-code-questio... →