Updated Installation (markdown)

Installation.md

@@ -25,10 +25,12 @@ Install dependencies:
 
     apt update && apt install libmono-cil-dev curl mediainfo
 
-Now proceed to [Manually Install Radarr](/Radarr/Radarr/wiki/Installation#manually-install-radarr) or use [Install on Debian 8 and Ubuntu 16.04](http://www.htpcguides.com/install-radarr-on-debian-8-jessie/).
+If you are on Ubuntu 18.04 or earlier, you'll need to update mono to the latest using [the official repository](https://www.mono-project.com/download/stable/#download-lin-ubuntu).
 
 If you are on Ubuntu 16.04 or earlier, you should also update your mediainfo to the latest using [the official releases](https://mediaarea.net/en/MediaInfo/Download/Ubuntu).
 
+Now proceed to [Manually Install Radarr](/Radarr/Radarr/wiki/Installation#manually-install-radarr) or use [Install on Debian 8 and Ubuntu 16.04](http://www.htpcguides.com/install-radarr-on-debian-8-jessie/).
+
 ### Fedora / CentOS ###
 
 Install dependencies (Fedora):