Error when running `spacy project document` on an old spaCy project

[ljvmiranda921]

I upgraded my spaCy version to 3.7.2, then reran spacy project document -o README.md to an older project (I don't remember when it was generated, maybe 2-3 months ago?). I encountered an error:

Traceback (most recent call last):
  File "/home/lj/.local/bin/spacy", line 8, in <module>
    sys.exit(setup_cli())
  File "/home/lj/.local/lib/python3.8/site-packages/spacy/cli/_util.py", line 87, in setup_cli
    command(prog_name=COMMAND)
  File "/home/lj/.local/lib/python3.8/site-packages/click/core.py", line 1130, in __call__
    return self.main(*args, **kwargs)
  File "/home/lj/.local/lib/python3.8/site-packages/typer/core.py", line 778, in main
    return _main(
  File "/home/lj/.local/lib/python3.8/site-packages/typer/core.py", line 216, in _main
    rv = self.invoke(ctx)
  File "/home/lj/.local/lib/python3.8/site-packages/click/core.py", line 1657, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/lj/.local/lib/python3.8/site-packages/click/core.py", line 1657, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/lj/.local/lib/python3.8/site-packages/click/core.py", line 1404, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/lj/.local/lib/python3.8/site-packages/click/core.py", line 760, in invoke
    return __callback(*args, **kwargs)
  File "/home/lj/.local/lib/python3.8/site-packages/typer/main.py", line 683, in wrapper
    return callback(**use_params)  # type: ignore
  File "/home/lj/.local/lib/python3.8/site-packages/weasel/cli/document.py", line 47, in project_document_cli
    project_document(project_dir, output_file, no_emoji=no_emoji)
  File "/home/lj/.local/lib/python3.8/site-packages/weasel/cli/document.py", line 115, in project_document
    "start": MARKER_START.format(marker_tag),
KeyError: 'tag'

I attempted a fix at #74