diff --git a/README.md b/README.md
index cc5ff41..7500b6f 100644
--- a/README.md
+++ b/README.md
@@ -40,18 +40,6 @@ conda activate zeeland
 pip install poetry
 ```
 
-Then you can run the client using the following command:
-
-```bash
-zeeland --help
-```
-
-or with `Poetry`:
-
-```bash
-poetry run zeeland --help
-```
-
 ### Basic Usage
 
 Create a metadata file in the default storage path.
@@ -82,6 +70,35 @@ if __name__ == "__main__":
     main()
 ```
 
+Singleton usage
+
+```python
+from zeeland import Singleton, singleton
+
+
+@singleton()
+class TestSingleton:
+    pass
+
+
+instance1 = TestSingleton()
+instance2 = TestSingleton()
+
+assert instance1 is instance2
+
+
+class TestSingletonWithArgs(metaclass=Singleton):
+    def __init__(self, value):
+        self.value = value
+
+
+instance1 = TestSingletonWithArgs("test1")
+instance2 = TestSingletonWithArgs("test2")
+
+assert instance1 is instance2
+assert instance1.value == "test1"
+```
+
 ### Makefile usage
 
 [`Makefile`](https://github.com/Undertone0809/zeeland/blob/main/Makefile) contains a lot of functions for faster development.
diff --git a/examples/singleton_usage.py b/examples/singleton_usage.py
new file mode 100644
index 0000000..9f4e4cc
--- /dev/null
+++ b/examples/singleton_usage.py
@@ -0,0 +1,24 @@
+from zeeland import Singleton, singleton
+
+
+@singleton()
+class TestSingleton:
+    pass
+
+
+instance1 = TestSingleton()
+instance2 = TestSingleton()
+
+assert instance1 is instance2
+
+
+class TestSingletonWithArgs(metaclass=Singleton):
+    def __init__(self, value):
+        self.value = value
+
+
+instance1 = TestSingletonWithArgs("test1")
+instance2 = TestSingletonWithArgs("test2")
+
+assert instance1 is instance2
+assert instance1.value == "test1"
diff --git a/setup.cfg b/setup.cfg
deleted file mode 100644
index 3c46a08..0000000
--- a/setup.cfg
+++ /dev/null
@@ -1,4 +0,0 @@
-[darglint]
-# https://github.com/terrencepreilly/darglint
-strictness = long
-docstring_style = google