Add <auto-generated> (#24)

src/ProxyInterfaceSourceGenerator/FileGenerators/ProxyClassesGenerator.cs

@@ -32,7 +32,7 @@ namespace ProxyInterfaceSourceGenerator.FileGenerators
             var constructorName = $"{targetClassSymbol.Name}Proxy";
 
             var file = new FileData(
-                $"{pd.FileName}Proxy.cs",
+                $"{pd.FileName}Proxy.g.cs",
                 CreateProxyClassCode(pd.Namespace, targetClassSymbol, interfaceName, className, constructorName)
             );
 
@@ -41,7 +41,17 @@ namespace ProxyInterfaceSourceGenerator.FileGenerators
             return file;
         }
 
-        private string CreateProxyClassCode(string ns, INamedTypeSymbol targetClassSymbol, string interfaceName, string className, string constructorName) => $@"using System;
+        private string CreateProxyClassCode(string ns, INamedTypeSymbol targetClassSymbol, string interfaceName, string className, string constructorName) => $@"//----------------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by https://github.com/StefH/ProxyInterfaceSourceGenerator.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//----------------------------------------------------------------------------------------
+
+#nullable enable
+using System;
 using AutoMapper;
 
 namespace {ns}
@@ -65,7 +75,8 @@ namespace {ns}
 
 {GeneratePrivateAutoMapper()}
     }}
-}}";
+}}
+#nullable disable";
         private string GeneratePrivateAutoMapper()
         {
             return _context.ReplacedTypes.Count == 0 ? string.Empty : "        private readonly IMapper _mapper;";