Make overview figure of all the different conversion/open/browser/cli function that do comparable things, but slightly differently

Other `README` required updates: 

- add the conversion overview figure
- The explanation of the 6-column data format only applies to CSV/df/parquet, not to geff/xml/CTC/etc. Make this clear by making a separate section
- start cli section with `open` not `convert`+`serve`
- proper docs?
