How to add license declaraction to my own program

[ZhangDonglin12]

Hello

how to add license.txt for using this repository: moonpdf

The license declaration as following shows:

Copyright (C) 2020  zhangdonglin12

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program.  If not, see <http://www.gnu.org/licenses/>.

Am I right to using this declaration for my program ?

Looking forward for your reply. Thanks .