additions, external link updates

entries/pixel_dungeon.md

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+# Pixel Dungeon
+
+- Home: http://pixeldungeon.watabou.ru/
+- State: mature, inactive since 2015
+- Download: https://f-droid.org//packages/com.watabou.pixeldungeon/
+- Platform: Windows, Linux, macOS, Android
+- Keyword: role playing, roguelike
+- Code repository: https://github.com/watabou/pixel-dungeon.git, https://github.com/watabou/PD-classes.git @add
+- Code language: Java
+- Code license: GPL-3.0
+
+## Building