doc typo: unnecessary backslashes to represent brackets in markdown (#11059)
There is a small typo in the doc which could mislead users: reference to
a table in `pyproject.toml` currently appears as
[`\[project.entry-points\]`](https://packaging.python.org/en/latest/guides/creating-and-discovering-plugins/#using-package-metadata)
while it should be
[`[project.entry-points]`](https://packaging.python.org/en/latest/guides/creating-and-discovering-plugins/#using-package-metadata).
Backslashes are appearing because they weren't supposed to be used on
code representation in Markdown.