Display copyright info, GPLv2, and other license info screens.

[redrumrobot]

First show copyright info for "Tremulous" and for the launcher/installer itself:
"Tremulous" copyright ©️ 2005-2015 Tim 'timbo' Angus with Darklegion Development, and the Tremulous development community.
Copyright ©️ 2016 GrangerHub

"Tremulous-Launcher" copyright ©️ 2016 Jeff Kent
Copyright ©️ 2016 GrangerHub

Game media for "Tremulous" released under Creative Commons Attribution-ShareAlike 3.0 (CC BY-SA 3.0 US) license.

Please see the file named COPYING for additional details and exemptions.

Next up, display the license and force the user to agree to proceed:
Show the GPL 2 plaintext of the license along with a scrollbar in UI. Display a grayed-out 'I have read and understand the terms and conditions of the license.' checkbox. Show a grayed-out "Next" button. Only after scrolling to the end of the text should the checkbox become available, and after they check it they can click "Next" to proceed with install.