all: add an example

Author: changkun

README.md

@@ -1,23 +1,16 @@
 # code2img [![PkgGoDev](https://pkg.go.dev/badge/golang.design/x/code2img)](https://pkg.go.dev/golang.design/x/code2img) ![](https://changkun.de/urlstat?mode=github&repo=golang-design/code2img)
 
-a carbon service wrapper
+a carbon service wrapper for Go users
 
 ```go
 import "golang.design/x/code2img"
 ```
 
 ## API Usage
 
-Just one API `code2img.Render`, to use it:
+Just one API `code2img.Render`, to use it (see [main.go](./example/main.go)):
 
-```go
-b, err := code2img.Render(context.TODO(), `import "golang.design/x/code2img"`)
-if err != nil {
-    panic(err)
-}
-
-os.WriteFile("code.png", b, os.ModePerm)
-```
+![](./example/code.png)
 
 ## Service Usage
 

code2img_test.go

@@ -22,7 +22,7 @@ func TestRender(t *testing.T) {
 	ctx, cancel := context.WithTimeout(context.Background(), time.Second*10)
 	defer cancel()
 
-	got, err := code2img.Render(ctx, `import "golang.design/x/code2img`)
+	got, err := code2img.Render(ctx, `import "golang.design/x/code2img"`)
 	if err != nil {
 		t.Fatalf("render failed: %v", err)
 	}

example/code.png

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"context"
+	"os"
+
+	"golang.design/x/code2img"
+)
+
+func main() {
+	f, err := os.ReadFile("main.go")
+	if err != nil {
+		panic(err)
+	}
+	code := string(f)
+
+	// render it!
+	b, err := code2img.Render(context.TODO(), code)
+	if err != nil {
+		panic(err)
+	}
+
+	os.WriteFile("code.png", b, os.ModePerm)
+}