func (r *Request) SetHeaders(headers map[string]string) *Request {
	for h, v := range headers {
		r.SetHeader(h, v)
	}
	return r
}
SetHeaders method sets multiple headers field and its values at one go in the current request.
Example: To set `Content-Type` and `Accept` as `application/json`

resty.R().
SetHeaders(map[string]string{
"Content-Type": "application/json",
"Accept": "application/json",
})
Also you can override header value, which was set at client instance level.
package resty
import (
	"encoding/base64"
	"encoding/json"
	"encoding/xml"
	"fmt"
	"io"
	"net"
	"net/url"
	"reflect"
	"strings"
)
type SRVRecord struct {
	Service string
	Domain  string
}
func (r *Request) SetHeader(header, value string) *Request {
	r.Header.Set(header, value)
	return r
}