Add single LEGAL file with license and copyright.

LEGAL

@@ -0,0 +1,21 @@
+This file is part of Telegram Desktop,
+the official desktop application for the Telegram messaging service.
+
+Copyright (c) 2014-2018 John Preston, https://desktop.telegram.org
+
+Telegram Desktop 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.
+
+It 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.
+
+In addition, as a special exception, the copyright holders give permission
+to link the code of portions of this program with the OpenSSL library.
+
+More information about the Telegram project: https://telegram.org
+
+Full license: https://github.com/telegramdesktop/tdesktop/blob/master/LICENSE

LICENSE

@@ -4,6 +4,7 @@ version 3 with the addition of the following special exception:
 In addition, as a special exception, the copyright holders give
 permission to link the code of portions of this program with the OpenSSL
 library.
+
 You must obey the GNU General Public License in all respects for all of
 the code used other than OpenSSL. If you modify file(s) with this
 exception, you may extend this exception to your version of the file(s),