add new ipcluster options to config template

starcluster/templates/config.py

@@ -272,9 +272,16 @@
 # latency message passing via ZeroMQ.
 # [plugin ipcluster]
 # SETUP_CLASS = starcluster.plugins.ipcluster.IPCluster
+# # Enable the IPython notebook server (optional)
 # ENABLE_NOTEBOOK = True
-# #set a password for the notebook for increased security
+# # Set a password for the notebook for increased security
+# # This is optional but *highly* recommended
 # NOTEBOOK_PASSWD = a-secret-password
+# # Set a custom directory for storing/loading notebooks (optional)
+# NOTEBOOK_DIRECTORY = /path/to/notebook/dir
+# # Set a custom packer. Must be one of 'json', 'pickle', or 'msgpack'
+# # This is optional.
+# PACKER = pickle
 #
 # Use this plugin to create a cluster SSH "dashboard" using tmux. The plugin
 # creates a tmux session on the master node that automatically connects to all