Add Fastlane metadata for F-Droid (#15411)

Co-authored-by: grorp <grorp@posteo.de>

fastlane/metadata/android/en-US/full_description.txt

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+Luanti is a voxel-based game platform with multiplayer capabilities.
+
+The objective of the available games varies, from sandbox games where you can explore, dig and build in a very large voxel world, to arcade-style games.
+
+There is a wide range of built-in map generators for procedurally generated terrain, and voxel-based lighting that adapts to the environment and light sources.
+
+All games and mods are written in Lua with a scripting API that is easy to use and makes it easy for modders to get started.

fastlane/metadata/android/en-US/short_description.txt

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+Voxel-based multiplayer game platform

fastlane/metadata/android/en-US/title.txt

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+Luanti