You can clone with
HTTPS or Subversion.
If I want to add new mapping candidates should they be added in the existing file? I don´t think so, because changing the file would change the content of a line and the references included in issues would be destroyed. But I am not really sure about this.
If I would include them by uploading another version of the file, how can the comments of two different versions be merged? If I raise an issue, should I include links to every version?