Update help link about Markdown

Closes gh-7428

IPython/html/templates/notebook.html

@@ -249,7 +249,7 b' data-notebook-path="{{notebook_path}}"'
                             sections = (
                                 (
                                     ("http://nbviewer.ipython.org/github/ipython/ipython/blob/2.x/examples/Index.ipynb", "Notebook Help", True),
-                                    ("http://help.github.com/articles/github-flavored-markdown","Markdown",True),
+                                    ("https://help.github.com/articles/markdown-basics/","Markdown",True),
                                 ),
                             )
                         %}