"follow" option: progressive generation of graph as data is added to CSV file

[hattesen]

It would be nice to have a --follow option, where graph-cli does not stop reading from the file (or stdin) when an EOF is reached, but instead waits (indefinitely) for more data to be appended to the CSV file and renders the graph as data appears.
Using the --follow option requires the user to manually terminate the graph-cli command.

It would likely require x-range to be explicitly defined and/or dynamically compress the x-axis as more data appears (or redrawing), which may not be supported by the graphing library.

A similar -f, --follow option is available in the Linux/Unix tail command