Update licensing and switch back to GPLv3 😅

Makefile

@@ -1,3 +1,18 @@
+# Copyright (C) 2025 Elaina Claus
+# 
+#     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/>.
+
 include := './include'
 
 mbr_source_files := $(wildcard src/mbr/*.nasm)