license: add Source Code Form License Notice

Author: lucor

AUTHORS

@@ -0,0 +1 @@
+Luca Corbo <paw@lucor.dev>

internal/agent/agent.go

@@ -1,3 +1,8 @@
+// Copyright 2023 the Paw Authors. All rights reserved.
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
 package agent
 
 import (