doc: update examples for custom templates

examples/entcpkg/README.md

@@ -12,23 +12,35 @@ package main
 
 import (
 	"log"
+	"strings"
+	"text/template"
 
 	"github.com/facebook/ent/entc"
 	"github.com/facebook/ent/entc/gen"
-	"github.com/facebook/ent/schema/field"
 )
 
 func main() {
+	// A usage for custom templates with external functions.
+	// One template is defined in the option below, and the
+	// second template is provided with the `Templates` field.
+	opts := []entc.Option{
+		entc.Funcs(template.FuncMap{"title": strings.ToTitle}),
+		entc.TemplateFiles("template/static.tmpl"),
+	}
 	err := entc.Generate("./schema", &gen.Config{
 		Header: `
 			// Copyright 2019-present Facebook Inc. All rights reserved.
 			// This source code is licensed under the Apache 2.0 license found
 			// in the LICENSE file in the root directory of this source tree.
 
-			// Code generated (@generated) by entc, DO NOT EDIT.
+			// Code generated by entc, DO NOT EDIT.
 		`,
-		IDType: &field.TypeInfo{Type: field.TypeInt},
-	})
+		Templates: []*template.Template{
+			template.Must(template.New("debug").
+				Funcs(gen.Funcs).
+				ParseFiles("template/debug.tmpl")),
+		},
+	}, opts...)
 	if err != nil {
 		log.Fatal("running ent codegen:", err)
 	}