added help line tointeractiveshell.py

IPython/terminal/interactiveshell.py

@@ -173,7 +173,12 b' class TerminalInteractiveShell(InteractiveShell):'
         help="Automatically set the terminal title"
     ).tag(config=True)
 
-    display_completions = Enum(('column', 'multicolumn','readlinelike'), default_value='multicolumn').tag(config=True)
+    display_completions = Enum(('column', 'multicolumn','readlinelike'), 
+        help= ( "Options for displaying tab completions, 'column', 'multicolumn', and"
+                "'readlinelike'. These options are for `prompt_toolkit`, see `prompt_toolkit`"
+                "documentation for more information."
+                ),
+        default_value='multicolumn').tag(config=True)
 
     highlight_matching_brackets = Bool(True,
         help="Highlight matching brackets .",