我想学习Sphinx，但卡在基础示例上了。在源代码目录中执行make html时，出现以下错误：
Running Sphinx v1.1.3
loading pickled environment... not yet created
building [html]: targets for 2 source files that are out of date
updating environment: 2 added, 0 changed, 0 removed
reading sources... [100%] intro
/home/owner/Desktop/doc/index.rst:11: ERROR: Error in "toctree" directive:
invalid option block.
.. toctree::
:maxdepth: 2
intro.rst
looking for now-outdated files... none found
pickling environment... done
checking consistency... /home/owner/Desktop/doc/intro.rst:: WARNING: document isn't included in any toctree
done
preparing documents... done
writing output... [100%] intro
writing additional files... genindex search
copying static files... done
dumping search index... done
dumping object inventory... done
build succeeded, 2 warnings.
Build finished. The HTML pages are in _build/html.
我还尝试过引用intro而不是intro.rst，但似乎都不起作用。index.rst和intro.rst在同一个目录中。我使用sphinx-quickstart创建了这个项目，并选择了所有默认选项。