Twenty Nineteen: Add missing copyright information.

Props poena, kjellr.
Fixes #47857.

git-svn-id: https://develop.svn.wordpress.org/trunk@45774 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-content/themes/twentynineteen/readme.txt

@@ -13,6 +13,21 @@ Our 2019 default theme is designed to show off the power of the block editor.
 == Description ==
 Our 2019 default theme is designed to show off the power of the block editor. It features custom styles for all the default blocks, and is built so that what you see in the editor looks like what you'll see on your website. Twenty Nineteen is designed to be adaptable to a wide range of websites, whether you’re running a photo blog, launching a new business, or supporting a non-profit. Featuring ample whitespace and modern sans-serif headlines paired with classic serif body text, it's built to be beautiful on all screen sizes.
 
+== Copyright ==
+
+Twenty Nineteen WordPress Theme, Copyright 2018 WordPress.org
+Twenty Nineteen is distributed under the terms of the GNU GPL
+
+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 2 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.
+
 == Changelog ==
 
 = 1.4 =