Golang regex get value inside parentheses

Question

Code:

package main

import (
    "fmt"
    "regexp"
)

func main() {
    r := regexp.MustCompile(`((.*))`)
    s := `(tag)SomeText`

    res := r.FindStringSubmatch(s)
    fmt.Println(res[1])
}

How to Get Value inside parentheses?