Mention that pcl-expect can collect stderr of a spawned program via a

pipe.

README

@@ -18,6 +18,9 @@ know about.)  This module has a few features that sets it apart:
      - a generic TCP session
      - a program started via Peter Årstrands popen5 module (FIXME: not
        yet implemented)
+     - a program started in a pty, but with the stderr of the program
+       collected via a pipe so that you can differentiate between
+       stdout and stderr.
 
  - Can spawn a program so that stdout is connected to a pty and stderr
    to a pipe, so that you can see the difference between them.