Add hardcoded fallback mountpoints for asset detection on Linux.

OpenRA.Mods.Common/Widgets/Logic/Installation/InstallFromDiscLogic.cs

@@ -118,6 +118,18 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 					.Where(IsValidDrive)
 					.Select(v => v.RootDirectory.FullName);
 
+				if (Platform.CurrentPlatform == PlatformType.Linux)
+				{
+					// Outside of Gnome, most mounting tools on Linux don't set DriveType.CDRom
+					// so provide a fallback by allowing users to manually mount images on known paths
+					volumes = volumes.Concat(new[]
+					{
+						"/media/openra",
+						"/media/" + Environment.UserName + "/openra",
+						"/mnt/openra"
+					});
+				}
+
 				foreach (var kv in sources)
 				{
 					message = "Searching for " + kv.Value.Title;