IPython/utils/_process_emscripten.py: Add file header

IPython/utils/_process_emscripten.py

@@ -1,12 +1,17 b''
+"""Emscripten-specific implementation of process utilities.
+
+This file is only meant to be imported by process.py, not by end-users.
+"""
+
 def system(cmd):
     raise OSError("Not available")
 
 def getoutput(cmd):
     raise OSError("Not available")
 
 def check_pid(cmd):
     raise OSError("Not available")
 
 def arg_split(s, posix=False, strict=True):
     """This one could be made to work but it's not clear if it would be useful..."""
     raise OSError("Not available")