address review comments

src/google/protobuf/compiler/csharp/csharp_source_generator_base.cc

@@ -56,8 +56,9 @@ SourceGeneratorBase::~SourceGeneratorBase() {
 
 void SourceGeneratorBase::WriteGeneratedCodeAttributes(io::Printer* printer) {
   printer->Print("[global::System.Diagnostics.DebuggerNonUserCodeAttribute]\n");
-  // We don't provide protoc info in the [GeneratedCode] attribute the because the
-  // pre-generated code in this repository would then have junk info in it.
+  // The second argument of the [GeneratedCode] attribute could be set to current protoc
+  // version, but that would cause excessive code churn in the pre-generated
+  // code in the repository every time the protobuf version number is updated.
   printer->Print("[global::System.CodeDom.Compiler.GeneratedCode(\"protoc\", null)]\n");
 }