[Update] documentation for errors

README.md

@@ -25,10 +25,14 @@ package main
 import "github.com/gouef/mode"
 
 func main()  {
-    m := mode.NewBasicMode()
+    m, err := mode.NewBasicMode()
+
+	if err != nil {
+		// do something
+    }
 
     // some code
-    if m.IsRelease() {
+    if r, _ := m.IsRelease(); r {
         // some code
     }
 }
@@ -40,19 +44,20 @@ func main()  {
 package main
 import "github.com/gouef/mode"
 
-modes := []string{"staging"}
-		mode := mode.NewMode(modes)
-
 func main()  {
 	modes := []string{"staging"}
-	m := mode.NewMode(modes)
+	m, err := mode.NewMode(modes)
+
+	if err != nil {
+		// do something
+	}
 
 	// some code
-	if m.IsRelease() {
+	if r, _ := m.IsRelease(); r {
 		m.EnableMode("staging")
 	}
 
-	if m.IsMode("staging") {
+	if sm, _ := m.IsMode("staging"); sm {
 		// some code
 	}
 }

mode.go

@@ -25,7 +25,7 @@ type Mode struct {
 // NewBasicMode create basic Mode with debug, release, test
 // Example:
 //
-//	mode := mode.NewBaseMode()
+//	mode, err := mode.NewBaseMode()
 func NewBasicMode() (*Mode, error) {
 	return NewMode(nil)
 }
@@ -34,7 +34,7 @@ func NewBasicMode() (*Mode, error) {
 // Example:
 //
 //	 modes := []string{"staging"}
-//		mode := mode.NewMode(modes)
+//	 mode, err := mode.NewMode(modes)
 func NewMode(additionalModes []string) (*Mode, error) {
 	mode := os.Getenv(EnvMode)
 	modes := []string{