Setuptools-scm causes documentation build to fail

[ambrosejcarr]

When attempting to build docs, setuptools-scm fails to load.

WARNING: autodoc: failed to import module 'setup'; the following exception was raised:
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/sphinx/ext/autodoc/importer.py", line 140, in import_module
    __import__(modname)
  File "/Users/ajc/projects/broadinstitute/cromwell-tools/setup.py", line 37, in <module>
    include_package_data=True
  File "/usr/local/lib/python3.6/site-packages/setuptools/__init__.py", line 129, in setup
    return distutils.core.setup(**attrs)
  File "/usr/local/Cellar/python/3.6.5/Frameworks/Python.framework/Versions/3.6/lib/python3.6/distutils/core.py", line 108, in setup
    _setup_distribution = dist = klass(attrs)
  File "/usr/local/lib/python3.6/site-packages/setuptools/dist.py", line 370, in __init__
    k: v for k, v in attrs.items()
  File "/usr/local/Cellar/python/3.6.5/Frameworks/Python.framework/Versions/3.6/lib/python3.6/distutils/dist.py", line 281, in __init__
    self.finalize_options()
  File "/usr/local/lib/python3.6/site-packages/setuptools/dist.py", line 529, in finalize_options
    ep.load()(self, ep.name, value)
  File "/usr/local/lib/python3.6/site-packages/setuptools_scm/integration.py", line 22, in version_keyword
    dist.metadata.version = get_version(**value)
  File "/usr/local/lib/python3.6/site-packages/setuptools_scm/__init__.py", line 119, in get_version
    parsed_version = _do_parse(root, parse)
  File "/usr/local/lib/python3.6/site-packages/setuptools_scm/__init__.py", line 97, in _do_parse
    "use git+https://github.com/user/proj.git#egg=proj" % root)
LookupError: setuptools-scm was unable to detect version for '/Users/ajc/projects/humancellatlas/sctools/docs'.

Make sure you're either building from a fully intact git repository or PyPI tarballs. Most other sources (such as GitHub's tarballs, a git checkout without the .git folder) don't contain the necessary metadata and will not work.

For example, if you're using pip, instead of https://github.com/user/proj/archive/master.zip use git+https://github.com/user/proj.git#egg=proj

Reproduce the error:

# checkout the branch where I'm fixing readthedocs; note the failure ALSO occurs on 
# master
g checkout ajc-docs-badge-add
cd docs
sphinx-build source/ build/