Fix Sphinx warnings

[hugovk]

Fixes https://github.com/gitpython-developers/gitdb/issues/71.

Two things:

• There is no .static dir in use, comment it out
• Docstrings usually need a new line between a summary and the params/return: https://sphinx-rtd-tutorial.readthedocs.io/en/latest/docstrings.html

$ python3 setup.py build_sphinx -b man
running build_sphinx
Running Sphinx v4.0.2
loading pickled environment... done
building [mo]: targets for 0 po files that are out of date
building [man]: all manpages
updating environment: 0 added, 0 changed, 0 removed
looking for now-outdated files... none found
writing... gitdb.1 { intro tutorial api algorithm changes } done
build succeeded.

The manual pages are in build/sphinx/man.

[Byron]

Thanks a lot, great initiative!