doc: Append pattern of configuration file

doc/advanced/config-file.rst

@@ -0,0 +1,43 @@
+=========================
+Extra configuration files
+=========================
+
+age supports other files excepted for `.age.toml` to manage configuration.
+
+Order of finding
+================
+
+age check "these are exiets" and "this includes configuration of age".
+It use first valid file for configuration .
+
+1. ``.age.toml``
+2. ``Cargo.toml``
+3. ``pyproject.toml``
+
+File and section
+================
+
+``.age.toml``
+-------------
+
+Standard configuration file of ``age``.
+
+Configuration values are managed on top-level sesciont.
+
+``Cargo.toml``
+--------------
+
+Manifest file of Rust project.
+
+``age`` refers ``package.metadata.age`` of file.
+
+.. note:: See spec of file on `"The Cargo Book" <https://doc.rust-lang.org/cargo/reference/manifest.html>`_.
+
+``pyproject.toml``
+------------------
+
+Metadata management file of Python project.
+
+``age`` refers ``tool.age`` of file.
+
+.. note:: See `spec of file <https://packaging.python.org/en/latest/specifications/pyproject-toml/>`_.

doc/advanced/index.rst

@@ -1,7 +1,11 @@
-===============
-Advanced usages
-===============
+==============
+Advanced usage
+==============
+
+There are some extra usecases.
 
 .. toctree::
+   :maxdepth: 2
 
    workspace
+   config-file