Add F-Droid badge

README.md

@@ -15,6 +15,7 @@ Current features:
 ## Download
 
 [![stable release](https://img.shields.io/badge/release-v0.1.2-blue.svg)](https://github.com/inorichi/tachiyomi/releases)
+[![fdroid release](https://img.shields.io/badge/release-F--Droid-blue.svg)](https://f-droid.org/repository/browse/?fdid=eu.kanade.tachiyomi)
 [![latest debug build](https://img.shields.io/badge/debug-latest%20build-blue.svg)](http://tachiyomi.kanade.eu/latest/app-debug.apk)
 
 ## License