The package and its documentation are on hex.pm.
If no configuration is specified, the API layer 57  will be used.
Although this library was only tested with the above layer version, you can
specify a custom source in you
config :telegram_tl, tl_path: "/path/to/mtproto.json", api_version: 57, api_path: "/path/to/api-layer-57.json"
 : the last documented version is API layer 23.