Added referenced CNC mod project to the solution

The "GenerateDocumentationFile" defined in Directory.Build.props would not work for projects that are referenced, but are not part of the solution, causing a warning
"CSC : warning SA0001: XML comment analysis is disabled due to project configuration (https://github.com/DotNetAnalyzers/StyleCopAnalyzers/blob/master/documentation/SA0001.md)",
which the CI treats as an error.

Mobius.sln

@@ -1,11 +1,14 @@
-
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio 2012
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OpenRA.Mods.Example", "OpenRA.Mods.Mobius\OpenRA.Mods.Mobius.csproj", "{4E5B38F7-4E99-4C92-BB39-9100CC7F3829}"
+# Visual Studio Version 17
+VisualStudioVersion = 17.7.34009.444
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "OpenRA.Mods.Mobius", "OpenRA.Mods.Mobius\OpenRA.Mods.Mobius.csproj", "{4E5B38F7-4E99-4C92-BB39-9100CC7F3829}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OpenRA.Game", "engine\OpenRA.Game\OpenRA.Game.csproj", "{0DFB103F-2962-400F-8C6D-E2C28CCBA633}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "OpenRA.Game", "engine\OpenRA.Game\OpenRA.Game.csproj", "{0DFB103F-2962-400F-8C6D-E2C28CCBA633}"
 EndProject
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "OpenRA.Mods.Common", "engine\OpenRA.Mods.Common\OpenRA.Mods.Common.csproj", "{FE6C8CC0-2F07-442A-B29F-17617B3B7FC6}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "OpenRA.Mods.Common", "engine\OpenRA.Mods.Common\OpenRA.Mods.Common.csproj", "{FE6C8CC0-2F07-442A-B29F-17617B3B7FC6}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "OpenRA.Mods.Cnc", "engine\OpenRA.Mods.Cnc\OpenRA.Mods.Cnc.csproj", "{69392273-3567-41BE-85E3-13222FD70E42}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -32,5 +35,14 @@ Global
 		{FE6C8CC0-2F07-442A-B29F-17617B3B7FC6}.Release|Any CPU.Build.0 = Release|Any CPU
 		{FE6C8CC0-2F07-442A-B29F-17617B3B7FC6}.Release-x86|Any CPU.ActiveCfg = Release|Any CPU
 		{FE6C8CC0-2F07-442A-B29F-17617B3B7FC6}.Release-x86|Any CPU.Build.0 = Release|Any CPU
+		{69392273-3567-41BE-85E3-13222FD70E42}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{69392273-3567-41BE-85E3-13222FD70E42}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{69392273-3567-41BE-85E3-13222FD70E42}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{69392273-3567-41BE-85E3-13222FD70E42}.Release|Any CPU.Build.0 = Release|Any CPU
+		{69392273-3567-41BE-85E3-13222FD70E42}.Release-x86|Any CPU.ActiveCfg = Release|Any CPU
+		{69392273-3567-41BE-85E3-13222FD70E42}.Release-x86|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
 	EndGlobalSection
 EndGlobal