Cannot Get TOCTREE in Sphinx to Show Link
You are getting this error because you don't have a title in intro.rst.
In order to fix this, add a title to intro.rst. Suppose you want your title to be My Title, then the title can be added by making the following two lines the first lines of intro.rst:
My Title*********Note that you must have enough * characters to completely underline your title, else you will get another error about a malformed title or underlining thereof.