Correct Next topic link for last page in documentation's Tutorial, Guides

[bertiewooster]

To agree with the ordering of the documentation home page, the Next topic link (in the left-side navigation bar) for the last page of a section should be the first page of the next section. Specifically, these pages do not follow that ordering:

• On the last page of Tutorial, the Next topic link should be to Guides.
• On the last page of Guides, the Next topic link should be to Explanation.

[bertiewooster]

Where is the Next topic link set? I examined the source of the content at e.g. https://github.com/sympy/sympy/blob/master/doc/src/tutorial/manipulation.rst and didn't find it there, nor did I find anything in conf.py.

[bertiewooster]

Figured it out--the topics use the order in the relevant Sphinx toctree, which in this case is doc/src/index.rst