Add BZFlag

[TheGiraffe3]

name: "BZFlag"
website_url: "https://bzflag.org"
source_code_url: "https://github.com/BZFlag-Dev/bzflag"
description: "Open-source multiplayer tank game around since the 1990s."
licenses:
  - LGPL
  - Mozilla 2.0
platforms:
  - C
  - C++
  - Perl
tags:
  - Games
depends_3rdparty: false
related_software_url: "https://forums.bzflag.org"

I am happy to make a pull request for this, but I'd like feedback on whether that would be acceptable first.

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[Ki-er]

Hi, thanks for the suggestions for this addition.

While this project has a release, it seems to be a while ago. We should wait for a newer release that is then over 4 months.