Add nullability to generated source

Author: DerekGooding

SimpleViewModel/SimpleViewModel.csproj

@@ -9,7 +9,7 @@
 
 	  <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
 	  <PackageId>SimpleViewModel</PackageId>
-	  <Version>0.9.5.2</Version>
+	  <Version>0.9.5.3</Version>
 	  <Authors>Derek Gooding</Authors>
 	  <Company>Derek Gooding</Company>
 	  <Description>

ViewModelGenerator/ViewModelGenerator.cs

@@ -56,7 +56,9 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
 
             // Generate ViewModel partial class
             var viewModelBuilder = new StringBuilder(
-$@"using SimpleViewModel.BaseClasses;
+$@"// <auto-generated />
+#nullable enable
+using SimpleViewModel.BaseClasses;
 
 namespace {namespaceName}
 {{
@@ -80,7 +82,9 @@ public partial class {className} : BaseViewModel
 
                     // Generate command class per method
                     var commandBuilder = new StringBuilder(
-$@"using SimpleViewModel.BaseClasses;
+$@"// <auto-generated />
+#nullable enable
+using SimpleViewModel.BaseClasses;
 
 namespace {namespaceName}
 {{