Add explanation of standard project structure (#8713)

Author: nothing-991

docs/pyproject.md

@@ -577,6 +577,24 @@ A list of packages and modules to include in the final distribution.
 If your project structure differs from the standard one supported by `poetry`,
 you can specify the packages you want to include in the final distribution.
 
+#### Standard Project Structure
+
+Poetry considers a "standard project structure" to be:
+
+```bash
+project_name/
+├── pyproject.toml
+├── README.md
+├── project_name/
+│   └── __init__.py
+└── tests/
+    └── __init__.py
+The top-level directory contains pyproject.toml and README.md.
+The main package directory matches the name field in pyproject.toml (or a snake_case variant).
+Tests go in a separate tests/ directory.
+{{% note %}} If your project matches this layout, Poetry will auto-detect your main package, and you do not need to list it in [tool.poetry.packages]. {{% /note %}}
+{{% warning %}} If your project differs from this standard layout — for example, packages inside a lib/ directory, or the top-level package name doesn’t match name in pyproject.toml — you must explicitly list them in [tool.poetry.packages] to include them in your distribution. {{% /warning %}}
+
 ```toml
 [tool.poetry]
 # ...