The OP has been created by the following command
cat README.md | piston post --author xeroc --permlink "piston-0-0-1" --category steem --title "[Release] Piston 0.0.1 - Command Line Tool for Steem"
while this reply has been created by:
piston reply --replyto "@xeroc/piston-0-0-1" --author xeroc --permlink "re-piston-0-0-1" --title "created by piston"
Now, have fun!