Copies files starting with ., add checks, improve documentation

• Files starting with "." in the source-directory are copied to the destination-repository-name. This has been the case in the master branch since December but it wasn't included in the previous release.
• Renamed the branches of this project's GitHub repositories to main, updated the documentation, etc. Note that the target-branch default value is still master for historical reasons, for now please set it to main if needed in your project.
• Updated documentation: this should help new users of the GitHub Action.

Thanks to everyone who opened issues, it has helped improving the GitHub Action (documentation or behaviour).

Apologies for the long time between releases: I have been very busy with other things.