Warnings in sphinx build

[apjanke]

Doing the make html sphinx build for the Guide is issuing a few warnings:

/Users/janke/local/repos/python-guide/docs/dev/virtualenvs.rst:221: WARNING: Title level inconsistent:

Basic Usage
~~~~~~~~~~~
/Users/janke/local/repos/python-guide/docs/dev/virtualenvs.rst:287: WARNING: Title level inconsistent:

Other Notes
~~~~~~~~~~~
/Users/janke/local/repos/python-guide/docs/scenarios/crypto.rst:4: WARNING: Duplicate explicit target name: "here".
/Users/janke/local/repos/python-guide/docs/scenarios/web.rst:534: WARNING: Footnote [1] is not referenced.
/Users/janke/local/repos/python-guide/docs/scenarios/web.rst:535: WARNING: Footnote [2] is not referenced.

[...]

checking consistency... /Users/janke/local/repos/python-guide/docs/404.rst: WARNING: document isn't included in any toctree