I recently got notification from GitHub support that they now allow Write access for uploading text files to Issues posts. This is welcome news.
Thanks to Dave McGill for testing this new feature.
This means that when you post an Issue you can attach your input file. But remember you need to append ".txt" to the file name. For example, if your input file is simple_test.fds, you need to change the name to simple_test.fds.txt or just simple_test.txt.