add magiskboot to license

Author: capntrips

LICENSE

@@ -35,3 +35,21 @@ which is licensed under the Apache 2.0 license:
     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     See the License for the specific language governing permissions and
     limitations under the License.
+
+This project bundles magiskboot (https://github.com/topjohnwu/Magisk),
+which is licensed under the GPLv3+ license:
+
+    Copyright (C) 2017-2022 John Wu <@topjohnwu>
+
+    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/>.