Update the LICENSE file.

* Add GLAD, used by the GL1 and GL3 renderers.
* Add zlib, because our unzip module is taken from zlib.

LICENSE

@@ -4,9 +4,11 @@ copys of each license:
 
 - Quake II
 - Info-ZIP
+- zlib
 - Cocoa SDL entry points
 - stb_image.h, stb_image_write.h, stb_image_resize.h, stb_vorbis.h
 - miniz
+- GLAD
 
 Parts of other Quake II Clients were included into the source. They're
 covered by the same GPLv2 license as Quake II itself:
@@ -437,6 +439,31 @@ freely, subject to the above disclaimer and the following restrictions:
 
 ===============================================================================
 
+Copyright notice:
+
+ (C) 1995-2024 Jean-loup Gailly and Mark Adler
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+
+  Jean-loup Gailly        Mark Adler
+  jloup@gzip.org          madler@alumni.caltech.edu
+
+===============================================================================
+
 Main entry point for our Cocoa-ized SDL app
 Initial Version: Darrell Walisser <dwaliss1@purdue.edu>
 Non-NIB-Code & other changes: Max Horn <max@quendi.de>
@@ -513,3 +540,69 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 THE SOFTWARE.
 
 ===============================================================================
+
+The glad source code:
+
+    The MIT License (MIT)
+
+    Copyright (c) 2013-2022 David Herberth
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy of
+    this software and associated documentation files (the "Software"), to deal in
+    the Software without restriction, including without limitation the rights to
+    use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+    the Software, and to permit persons to whom the Software is furnished to do so,
+    subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in all
+    copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+    FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+    COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+    IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+    CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+
+The Khronos Specifications:
+
+    Copyright (c) 2013-2020 The Khronos Group Inc.
+
+    Licensed under the Apache License, Version 2.0 (the "License");
+    you may not use this file except in compliance with the License.
+    You may obtain a copy of the License at
+
+        http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    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.
+
+
+The EGL Specification and various headers:
+
+    Copyright (c) 2007-2016 The Khronos Group Inc.
+
+    Permission is hereby granted, free of charge, to any person obtaining a
+    copy of this software and/or associated documentation files (the
+    "Materials"), to deal in the Materials without restriction, including
+    without limitation the rights to use, copy, modify, merge, publish,
+    distribute, sublicense, and/or sell copies of the Materials, and to
+    permit persons to whom the Materials are furnished to do so, subject to
+    the following conditions:
+
+    The above copyright notice and this permission notice shall be included
+    in all copies or substantial portions of the Materials.
+
+    THE MATERIALS ARE PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+    IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+    TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+    MATERIALS OR THE USE OR OTHER DEALINGS IN THE MATERIALS.
+
+===============================================================================