renamed games folder to entries folder (also contained frameworks, libraries, ...) and added to the backlog

entries/ufo_alien_invasion.md

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+# UFO: Alien Invasion
+
+_UFO: Alien Invasion is a squad-based tactical strategy game in the tradition of the old X-COM PC games_
+
+- Home: https://ufoai.org/wiki/News, https://sourceforge.net/projects/ufoai/
+- Media: <https://en.wikipedia.org/wiki/UFO:_Alien_Invasion>
+- State: mature
+- Download: https://ufoai.org/wiki/Download
+- Keywords: strategy, clone, inspired by X-COM series, turn-based
+- Code repository: https://github.com/ufoai/ufoai.git (mirror), https://git.code.sf.net/p/ufoai/code
+- Code language: C, C++
+- Code license: GPL-2.0
+
+## Building
+
+- Build system: CMake
+