Update 1) `generate_sn_data.py` : now the user can input any Hubble diagram and covariance matrix with inline arguments on the fly. Without needing to download the default DDF_10yrs data and associated covariance matrix etc and generate the `sacc` output file.
Update 2) Added README.md which defines how to input arguments for any custom SN input data files with `generate_sn_data.py` and generate their `sacc` file.
Update 3) Added a `sn_only.ini` file with a corresponding `snonly_values.ini` for an SN-only example script.