update doc and test

README.md

@@ -3,9 +3,10 @@
 ![Go Report Card](https://goreportcard.com/badge/github.com/yiling-j/piper?style=flat-square)
 
 - **Single Source of Truth**
-- **Code Generation, No Typo**
+- **Generated Key Structs, No Typo**
 - **Config Inheritance**
 - **Multiple Config Strategies Support**
+- **Cache For Better Performance**
 
 ## Why Piper
 If you are familiar with Django, this is how Django settings module looks like:
@@ -125,9 +126,12 @@ import (
 var configFS embed.FS
 
 os.Setenv("SECRET", "qux")
-piper.Load("config/stage.toml")
+// make sure turn on AutomaticEnv first then loading config,
+// this way the env vaiable is also cached, so IGet* methods can work properly
 piper.V().AutomaticEnv()
+piper.Load("config/stage.toml")
 secret := piper.GetString(config.Secret)
+
 ```
 
 ### Strategy III -  Copy config directory

integration/config_test.go

@@ -152,7 +152,7 @@ func TestMultiPiper(t *testing.T) {
 
 }
 
-func TestEnvOverride(t *testing.T) {
+func TestEnvOverrideI(t *testing.T) {
 	piper.Reset()
 	err := piper.Load("config_toml_multi/test.toml")
 	require.Nil(t, err)
@@ -164,6 +164,18 @@ func TestEnvOverride(t *testing.T) {
 	require.Equal(t, piper.IGetString(configtm.Foo), "test")
 }
 
+func TestEnvOverrideII(t *testing.T) {
+	piper.Reset()
+	piper.V().AutomaticEnv()
+	err := os.Setenv("FOO", "bar")
+	require.Nil(t, err)
+	err = piper.Load("config_toml_multi/test.toml")
+	require.Nil(t, err)
+
+	require.Equal(t, piper.GetString(configtm.Foo), "bar")
+	require.Equal(t, piper.IGetString(configtm.Foo), "bar")
+}
+
 func BenchmarkGet(b *testing.B) {
 	piper.Reset()
 	err := piper.Load("config_yaml_multi/test.yaml")