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Why are the installation instructions aimed towards Linux?
(sh.itjust.works)
F-Droid is an installable catalogue of FOSS (Free and Open Source Software) applications for the Android platform. The client makes it easy to browse, install, and keep track of updates on your device.
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They just didn't document how to do it on Android.
Using Play is probably the least safe way to install apps, which has been recently shown to have plenty of malicious apps.
Edit: They documented what it typically looks like on Linux. To document how to do it elsewhere would require recommending an app to do it with.
Would you trust that recommendation?