added Licensing

LICENSE

@@ -0,0 +1,17 @@
+TicTacToe - Simple Console TicTacToe
+
+Copyright (C) 2026 Jannis Heydemann
+  https://gitea.starfour.de/Jannis
+  http://www.github.com/JannisHeydemann
+
+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 <https://www.gnu.org/licenses/>.

TicTacToe.c

@@ -1,3 +1,6 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+// Copyright (C) 2026 Jannis Heydemann
+
 #include <stdio.h>
 #include <stdlib.h>
 char cPlayfield[3][3] = {