eof character (Ctrl-D) required even if input is just a file

[Nitrodist]

Most command line tools that I've used allow you to pass in data from standard in and signal the end of input with the eof character (ctrl-d) or they allow you to pass in the data from a file and in that case you don't need to send the eof character.

As far as I can tell, the cfn-graph program waits for the eof character even if I've passed it a file via the filename as a command line argument. The program should process the file if it's been passed without requiring the user to send the eof character, imo.

Alternatively, this behavior should be in the readme and command line help.