Make sure man pages are part of sdist tarball

The current tarball when uploaded to pypi via github actions
does not contain the manual pages because the doc target to
build them is not called. This commit runs the doc tox target
which is called prior pypi release. This Fixes #38

.github/workflows/ci-publish-to-pypi.yml

@@ -25,7 +25,7 @@ jobs:
         python -m pip install tox
     - name: Prepare
       run: |
-        tox -e release
+        tox -e doc,release
     - name: Publish
       uses: pypa/gh-action-pypi-publish@master
       with: