add docs to the codegen/ directory

codegen/.libcst.codemod.yaml

@@ -1,5 +1,11 @@
 generated_code_marker: "@generated"
-formatter: ["./.venv/bin/ruff", "format", "--stdin-filename=__generated__.pyi", "-"]
 blacklist_patterns: []
-modules: ["libcst.codemod.commands", "codegen.mods"]
 repo_root: "."
+formatter:
+  - "./.venv/bin/ruff"
+  - "format"
+  - "--stdin-filename=__generated__.pyi"
+  - "-"
+modules:
+  - "libcst.codemod.commands"
+  - "codegen.mods"

codegen/README.md

@@ -0,0 +1,19 @@
+# `scipy-stubs/codegen`
+
+To run a codemod, ensure that you are in the root directory of the `scipy-stubs` repository and run:
+
+```bash
+poe codemod $NAME
+```
+
+where `$NAME` is the name is the name of the codemod, which can be one of:
+
+- `AnnotateMissing` - Sets the default return type to `None`, and sets the other missing annotations to `scipy._typing.Untyped`.
+- `FixTrailingComma` - Adds a trailing comma to parameters that don't fit on one line, so that ruff formats them correctly.
+
+> [!NOTE]
+> The codemods require `libcst`, which is installable through the **optional** `codegen` dependency group:
+>
+> ```bash
+> poetry install --with=codegen
+> ```

codegen/mods.py

@@ -55,7 +55,7 @@ def leave_Module(self, original_node: cst.Module, updated_node: cst.Module) -> c
 
 @final
 class AnnotateMissing(_BaseMod):
-    DESCRIPTION = "Sets the default return type to `None`, and other missing annotations to `scipy._typing.Untyped`"
+    DESCRIPTION = "Sets the default return type to `None`, and sets the other missing annotations to `scipy._typing.Untyped`."
 
     untyped: Final[str]