additions (from f-droid) and some link updates

entries/zen.md

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+# Zen!
+
+- Home: https://web.archive.org/web/20200219170600/http://juankysoriano.com/zen
+- State: mature
+- Download: https://f-droid.org/de/packages/zen.meditation.android/
+- Platform: Android
+- Keyword: simulation
+- Code repository: https://github.com/juankysoriano/Zen.git
+- Code language: Java
+- Code license: GPL-2.0
+
+## Building
+
+- Build system: Gradle