fixed Notebook Help item as specified by ellisonbg

IPython/html/templates/notebook.html

@@ -248,7 +248,7 b' data-notebook-path="{{notebook_path}}"'
                         {% set
                             sections = (
                                 (
-                                    ("http://nbviewer.ipython.org/github/ipython/ipython/blob/2.x/examples/Index.ipynb", "Notebook Help", True),
+                                    ("http://nbviewer.ipython.org/github/ipython/ipython/blob/master/examples/Notebook/Index.ipynb", "Notebook Help", True),
                                     ("https://help.github.com/articles/markdown-basics/","Markdown",True),
                                 ),
                             )