error on pip install: 'ModuleNotFoundError: No module named 'markdown''

[sbenthall]

pip installing the current bigbang package in a clean environment gets the following erro. Related to #569

$ pip install bigbang
Collecting bigbang
  Downloading bigbang-0.1.9.tar.gz (1.3 kB)
  Preparing metadata (setup.py) ... error
  error: subprocess-exited-with-error

  × python setup.py egg_info did not run successfully.
  │ exit code: 1
  ╰─> [8 lines of output]
      Traceback (most recent call last):
        File "<string>", line 2, in <module>
        File "<pip-setuptools-caller>", line 34, in <module>
        File "/tmp/pip-install-f4kta6az/bigbang_190e627b8d66406ebcb4f5db4f83189e/setup.py", line 2, in <module>
          from bigbang import __version__ as version
        File "/tmp/pip-install-f4kta6az/bigbang_190e627b8d66406ebcb4f5db4f83189e/bigbang/__init__.py", line 1, in <module>
          from markdown import markdown
      ModuleNotFoundError: No module named 'markdown'
      [end of output]

  note: This error originates from a subprocess, and is likely not a problem with pip.
error: metadata-generation-failed

× Encountered error while generating package metadata.
╰─> See above for output.

note: This is an issue with the package mentioned above, not pip.
hint: See above for details.
WARNING: You are using pip version 22.0.4; however, version 23.0.1 is available.
You should consider upgrading via the '/home/sb/projects/tmp/bigbing-pip-test/bigbang-tmp-venv/bin/python3 -m pip install --upgrade pip' command.