Update README.md

Added further instructions as per the current status of yarl#84.

README.md

@@ -43,6 +43,20 @@ sudo apt-get install openjfx
 on your terminal.
 You can also check this link: https://pkgs.org/download/openjfx for more information on ```openjfx``` package for these distributions.
 
+Starting with Ubuntu 18.10 (and around the same time in Debian Sid), openjfx version 8 is no more available. Though it is possible to force the openjfx to stay in version 8, and run pattypan, this is pretty much a hack. If you still wish to proceed, you can run: 
+
+```
+apt purge openjfx
+apt install openjfx=8u161-b12-1ubuntu2 libopenjfx-jni=8u161-b12-1ubuntu2 libopenjfx-java=8u161-b12-1ubuntu2
+apt-mark hold openjfx libopenjfx-jni libopenjfx-java
+```
+
+If this still doesn't work, you may need to add the following line to you `/etc/apt/sources.list` file before running it again:
+
+```
+deb-src http://fr.archive.ubuntu.com/ubuntu/ bionic universe multiverse
+```
+
 ### License
 Copyright (c) 2016 Paweł Marynowski.