Added a note on a 'Open with' script for Touch Lux 3

install/Installation-on-PocketBook-devices.md

@@ -5,6 +5,7 @@ You need to obtain a recent PocketBook package from [this page](https://github.c
     1. copy and merge the `applications` directory in the unzipped archive into your PocketBook's USB root directory
 1. Associate PDF/DJVU/EPUB/FB2 documents to Koreader (optional)
     1. copy and merge the `system` directory in the unzipped archive into your PocketBook's USB root directory
+    1. Note: Pocketbook Touch Lux 3 (and possibly other models) require a more sophisticated method in the form of a script. See [this comment](https://github.com/koreader/koreader/issues/3544#issuecomment-396253917).
 1. Install Stardict dictionaries (optional)
     1. Copy Stardict format dictionary files (*.idx, *.ifo, *.dict) into the `applications/koreader/data/dict` directory.
 1. Install Tesseract language data (optional)