Introduce a note about FDroid version in order for anyone who would try to apply the patch to this version not to waste the time wondering why it wasn't working

User-patches.md

@@ -20,6 +20,9 @@ Names starting with:
 * `8` are executed before exit and before settings get saved,
 * `9` are executed right before exit.
 
+# Known limitations
+* On Android user patches don't work in the [FDroid version of KOReader](https://f-droid.org/en/packages/org.koreader.launcher.fdroid/). The package id for such version is `org.koreader.launcher.fdroid` and it is installed either from FDroid application or using the apk file available at the mentioned page. You have to manually install the release version that has the package id `org.koreader.launcher`
+
 # Available_patches
 
 (https://github.com/koreader/koreader/issues?q=+label%3A%22User+patch+available%22+)