Clarify why we use chmod instead of mkfifo's mode parameter

pipe_io_server/pipe.py

@@ -9,7 +9,7 @@ class Pipe:
     def recreate(self, permissions):
         self.remove()
         mkfifo(self.path)
-        chmod(self.path, permissions)
+        chmod(self.path, permissions)  # use chmod to ignore umask
 
     def remove(self):
         if exists(self.path):