feat(coding-guidelines): add guideline for ros node directory structure

docs/contributing/coding-guidelines/ros-nodes/directory-structure.md

@@ -3,3 +3,58 @@
 !!! warning
 
     Under Construction
+
+## C++ package
+
+```txt
+<package_name>
+├─ config
+│   ├─ foo_ros.param.yaml
+│   └─ foo_non_ros.yaml
+├─ include
+│   └─ <package_name>
+│      └─ foo_public.hpp
+├─ launch
+│   ├─ foo.launch.xml
+│   └─ foo.launch.py
+├─ src
+│   ├─ foo_node.cpp
+│   ├─ foo_node.hpp
+│   └─ foo_private.hpp
+├─ test
+│   └─ test_foo.cpp
+├─ package.xml
+└─ CMakeLists.txt
+```
+
+### config directory
+
+Place configuration files such as node parameters.
+
+For ROS parameters, use the extension `.param.yaml`.
+For non-ROS parameters, use the extension `.yaml`.
+
+Rationale: Since ROS parameters files are type-sensitive, they should not be the target of some code formatters and linters. In order to distinguish the file type, we use different file extensions.
+
+### include directory
+
+Place header files exposed to other packages. Do not place files directly under the `include` directory, but place files under the directory with the package name.
+This directory is used for mostly library headers. Note that many headers do not need to be placed here. It is enough to place the headers under the `src` directory.
+
+Reference: <https://docs.ros.org/en/rolling/How-To-Guides/Ament-CMake-Documentation.html#adding-files-and-headers>
+
+### launch directory
+
+Place launch files (`.launch.xml` and `.launch.py`).
+
+### src directory
+
+Place source files and private header files.
+
+### test directory
+
+Place source files for testing.
+
+## Python package
+
+T.B.D.