A User Manual can be found here
This package is available via packagist.org. Please use Composer to install the extension
bin/magento deploy:mode:set developer (if you are in production mode)
composer require fooman/emailattachments-m2:^3.0
bin/magento module:enable --clear-static-content Fooman_EmailAttachments
bin/magento setup:upgrade
your usual sequence of commands to enable production mode, for example
bin/magento deploy:mode:set production
If you are using Email Attachments to build functionality on top of please require the implementation package
composer require emailattachments-implementation-m2 instead as only that package will be semantically versioned.