binary: Accepts piped input from stdin. Fixes #448

Issues
---
- [x] no output when the file being `cat`'d is blank
- [x] we should document the usage of this feature in the readme

Fixes #448 
If we were to move this inside of `cli`, it would read `args.length === 0`. However, it mostly like makes sense here as the bin file is about collecting input and passing it to the cli. 

@mrjoelkemp perhaps you can add a comment explaining why you're looking exactly for 2.