Merge pull request #16 from wolfogre/dev

docs: complate README.md

README.md

@@ -6,4 +6,96 @@
 [![GitHub go.mod Go version](https://img.shields.io/github/go-mod/go-version/wolfogre/gtag)](https://github.com/wolfogre/gtag/blob/master/go.mod)
 [![GitHub tag (latest by date)](https://img.shields.io/github/v/tag/wolfogre/gtag)](https://github.com/wolfogre/gtag/releases)
 
-\[WIP\] Get field tag in an elegant way.
+Help you to get golang struct's tags elegantly.
+
+## Installing
+
+Install gtag by running:
+
+```bash
+go get -u github.com/wolfogre/gtag/cmd/gtag
+```
+
+and ensuring that `$GOPATH/bin` is added to your `$PATH`.
+
+## Tutorial
+
+### 1. define your struct
+
+A source file `user.go`:
+
+```go
+package tutorial
+
+type User struct {
+	Id    int    `bson:"_id"`
+	Name  string `bson:"name"`
+	Email string `bson:"email"`
+}
+```
+
+## 2. run gtag
+
+Run
+
+```bash
+gtag -types User -tags bson .
+```
+
+and you will get file user_tag.go:
+
+```go
+// Code generated by gtag. DO NOT EDIT.
+// See: https://github.com/wolfogre/gtag
+
+//go:generate gtag -types User -tags bson .
+package tutorial
+
+import "reflect"
+
+var (
+	// ...
+)
+
+type UserTags struct {
+	Id    string
+	Name  string
+	Email string
+}
+
+func (User) Tags(tag string) UserTags {
+	return UserTags{
+		Id:    tagOfUserId.Get(tag),
+		Name:  tagOfUserName.Get(tag),
+		Email: tagOfUserEmail.Get(tag),
+	}
+}
+
+func (v User) TagsBson() UserTags {
+	return v.Tags("bson")
+}
+```
+
+## 3. use it
+
+Now you can use the generated code to get tags elegantly:
+
+```go
+// update mongo document
+tags := User{}.TagsBson()
+
+_, err := collection.UpdateOne(
+    ctx,
+    bson.M{tags.Id: id},
+    bson.M{
+        "$set", bson.M{
+            tags.Name: name,
+            tags.Email: email,
+        },
+    },
+)
+```
+
+## Project status
+
+Gtag is beta and is considered feature complete.

test/internal/tutorial/user.go

@@ -0,0 +1,8 @@
+// user.go
+package tutorial
+
+type User struct {
+	Id    int    `bson:"_id"`
+	Name  string `bson:"name"`
+	Email string `bson:"email"`
+}