allow passing pipeline on stdin

hellpipe/main.py

@@ -30,6 +30,9 @@ def split_commands(tokens):
 
 def main():
     command = sys.argv[1] if len(sys.argv) > 1 else INPUTCMD
+    if command.strip() == "-":
+        command = sys.stdin.read()
+
     oneliner = shlex.shlex(command, posix=True, punctuation_chars=True)
     stages = []