add unrar package per requests, for subzero plugin

Dockerfile

@@ -18,6 +18,7 @@ RUN \
  apt-get install -y \
 	avahi-daemon \
 	dbus \
+	unrar \
 	wget && \
 
 # install plex

README.md

@@ -100,6 +100,7 @@ Valid settings for VERSION are:-
 
 ## Versions
 
++ **28.05.17:** Add unrar package as per requests, for subzero plugin.
 + **11.01.17:** Use Plex environemt variables from pms docker,
 change abc home folder to /app to alleviate usermod chowning library folder by default (thanks gbooker, plexinc).
 + **03.01.17:** Use case insensitive version variable matching rather than export and make lowercase.