Add .gitattributes file and mention workaround for DNS issues from internet provider

Kieran had some issues when working on AutoFeedback from Windows, due to how Git handles CR/LF newlines in some configurations, and also had some connectivity problems with the Packagist repositories used by Composer.

The first issue was solved by adding a .gitattributes file, ensuring that .sh files used only LF newlines.

The connectivity issues were caused by his internet provider's DNS infrastructure, and needed to be solved by overriding the DNS configuration in the Docker daemon.