fix: empty doc for bare built bento

[xianml]

What does this PR address?

Fix exception for build/push bento in codespace

stack trace

Traceback (most recent call last):
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/bin/bentoml", line 8, in <module>
    sys.exit(cli())
             ^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/lib/python3.11/site-packages/click/core.py", line 1157, in __call__
    return self.main(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/lib/python3.11/site-packages/click/core.py", line 1078, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/lib/python3.11/site-packages/click/core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/lib/python3.11/site-packages/click/core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/lib/python3.11/site-packages/click/core.py", line 783, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/BentoML/src/bentoml_cli/utils.py", line 364, in wrapper
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/BentoML/src/bentoml_cli/utils.py", line 335, in wrapper
    return_value = func(*args, **kwargs)
                   ^^^^^^^^^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/lib/python3.11/site-packages/simple_di/__init__.py", line 139, in _
    return func(*_inject_args(bind.args), **_inject_kwargs(bind.kwargs))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/BentoML/src/bentoml_cli/deployment.py", line 296, in develop_command
    deployment = create_deployment(
                 ^^^^^^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/lib/python3.11/site-packages/simple_di/__init__.py", line 139, in _
    return func(*_inject_args(bind.args), **_inject_kwargs(bind.kwargs))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/BentoML/src/bentoml_cli/deployment.py", line 885, in create_deployment
    config_params.verify()
  File "/Users/xian/Downloads/workspace/bentoml/src/BentoML/src/bentoml/_internal/cloud/deployment.py", line 185, in verify
    bento_info = ensure_bento(
                 ^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/lib/python3.11/site-packages/simple_di/__init__.py", line 139, in _
    return func(*_inject_args(bind.args), **_inject_kwargs(bind.kwargs))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/BentoML/src/bentoml/_internal/cloud/deployment.py", line 350, in ensure_bento
    bento_api.push(bento=bento_obj, bare=bare)
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/lib/python3.11/site-packages/simple_di/__init__.py", line 139, in _
    return func(*_inject_args(bind.args), **_inject_kwargs(bind.kwargs))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/BentoML/src/bentoml/_internal/cloud/bento.py", line 76, in push
    self._do_push_bento(
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/lib/python3.11/site-packages/simple_di/__init__.py", line 139, in _
    return func(*_inject_args(bind.args), **_inject_kwargs(bind.kwargs))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/BentoML/src/bentoml/_internal/cloud/bento.py", line 161, in _do_push_bento
    description=bento.doc,
                ^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/BentoML/src/bentoml/_internal/bento/bento.py", line 552, in doc
    with self._fs.open(BENTO_README_FILENAME, "r") as readme_md:
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/lib/python3.11/site-packages/fs/osfs.py", line 643, in open
    with convert_os_errors("open", path):
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/lib/python3.11/site-packages/fs/error_tools.py", line 89, in __exit__
    reraise(fserror, fserror(self._path, exc=exc_value), traceback)
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/lib/python3.11/site-packages/six.py", line 718, in reraise
    raise value.with_traceback(tb)
  File "/Users/xian/Downloads/workspace/bentoml/src/awesome-ai-apps-internal/.venv/lib/python3.11/site-packages/fs/osfs.py", line 647, in open
    return io.open(
           ^^^^^^^^
fs.errors.ResourceNotFound: resource 'README.md' not found

Fixes #(issue)

Before submitting:

• Does the Pull Request follow Conventional Commits specification naming? Here are GitHub's
  guide on how to create a pull request.
• Does the code follow BentoML's code style, pre-commit run -a script has passed (instructions)?
• Did you read through contribution guidelines and follow development guidelines?
• Did your changes require updates to the documentation? Have you updated
  those accordingly? Here are documentation guidelines and tips on writting docs.
• Did you write tests to cover your changes?

[github-actions]

Package	Statements
bentoml	55.40% (9886 / 17843)
Summary	55.40% (9886 / 17843)