Add GPLv3

src/EthIpUdp.zig

@@ -1,3 +1,19 @@
+// Copyright 2026 Robby Zambito
+//
+// This file is part of zaprus.
+//
+// Zaprus 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.
+//
+// Zaprus 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
+// Zaprus. If not, see <https://www.gnu.org/licenses/>.
+
 pub const EthIpUdp = packed struct(u336) { // 42 bytes * 8 bits = 336
     // --- UDP (Last in memory, defined first for LSB->MSB) ---
     udp: packed struct {