update: README.md

Author: 54m

README.md

@@ -1,2 +1,80 @@
 # structs
 structure utils
+
+# What is this?
+Look for struct fields that are nil.
+Used when the argument passed to the constructor etc. is a structure etc.
+
+# Usage
+
+### GetNilFields
+
+```go
+package main
+
+import (
+	"log"
+
+	"github.com/go-utils/structs"
+)
+
+type (
+	Repository1 struct{}
+	Repository2 struct{}
+	Repository3 struct{}
+)
+
+type ServiceRepositories struct {
+	Repository1 *Repository1
+	Repository2 *Repository2
+	Repository3 *Repository3
+}
+
+type Service struct {
+	repos ServiceRepositories
+}
+
+func NewService(repos ServiceRepositories) *Service {
+	if nilFields := structs.GetNilFields(repos); len(nilFields) > 0 {
+		log.Fatalf("%+v", nilFields)
+		// Output: ["ServiceRepositories.Repository2", "ServiceRepositories.Repository3"]
+	}
+	return &Service{repos: repos}
+}
+
+func main() {
+	repos := ServiceRepositories{
+		Repository1: new(Repository1),
+	}
+	service := NewService(repos)
+	...
+}
+```
+
+---
+
+### GetStructName
+
+```go
+package main
+
+import (
+	"fmt"
+	"log"
+
+	"github.com/go-utils/structs"
+)
+
+type Hoge struct{}
+
+func main() {
+	hoge := new(Hoge)
+	hogeName := structs.GetStructName(hoge)
+	fmt.Printf("struct name: %#v\n", hogeName)
+	// Output: "Hoge"
+}
+```
+
+## License
+- Under the [MIT License](./LICENSE)
+- Copyright (C) 2022 go-utils