在Google App Engine中托管Go项目时，应该如何处理文件路径？ 打开templates / index.html：没有这样的文件或目录

I am trying to deploy a simple go language code on Google's app engine. This is the code I am trying to deploy. https://github.com/GoogleCloudPlatform/golang-samples/tree/master/appengine/go11x/static

main.go

package main

import (
    "fmt"
    "html/template"
    "log"
    "net/http"
    "os"
    "path/filepath"
    "time"
)

var (
    indexTmpl = template.Must(
        template.ParseFiles(filepath.Join("templates", "index.html")),
    )
)

func main() {
    http.HandleFunc("/", indexHandler)

    // Serve static files out of the public directory.
    // By configuring a static handler in app.yaml, App Engine serves all the
    // static content itself. As a result, the following two lines are in
    // effect for development only.
    public := http.StripPrefix("/public", http.FileServer(http.Dir("public")))
    http.Handle("/public/", public)

    port := os.Getenv("PORT")
    if port == "" {
        port = "8080"
        log.Printf("Defaulting to port %s", port)
    }

    log.Printf("Listening on port %s", port)
    log.Fatal(http.ListenAndServe(fmt.Sprintf(":%s", port), nil))
}

// indexHandler uses a template to create an index.html.
func indexHandler(w http.ResponseWriter, r *http.Request) {
    if r.URL.Path != "/" {
        http.NotFound(w, r)
        return
    }
    type indexData struct {
        Logo        string
        Style       string
        RequestTime string
    }
    data := indexData{
        Logo:        "/public/gcp-gopher.svg",
        Style:       "/public/style.css",
        RequestTime: time.Now().Format(time.RFC822),
    }
    if err := indexTmpl.Execute(w, data); err != nil {
        log.Printf("Error executing template: %v", err)
        http.Error(w, "Internal server error", http.StatusInternalServerError)
    }
}

When I deploy this code using gcloud app deploy and use the browser to load the webpage, I see error

2019-08-24 06:32:19 default[]  "GET / HTTP/1.1" 500
2019-08-24 06:32:20 default[]  panic: open templates/index.html: no such file or directory    goroutine 1 [running]:  html/template.Must(0x0, 0x800800, 0xc000078f90, 0
x0)     /usr/local/go/src/html/template/template.go:372 +0x54

My app.yaml file looks like this. It has static mentioned but nothing about templates.

runtime: go111
handlers:
# Configure App Engine to serve any static assets.
- url: /public
  static_dir: public
# Use HTTPS for all requests.
- url: /.*
  secure: always
  redirect_http_response_code: 301
  script: auto

Question: How do I handle templates and other small files that I want the application to read? Mine is a toy application so I do not need cloud storage or any such solution. I just want to read from a (local) directory.