THRIFT-4705: add nuget configuration file
diff --git a/lib/csharp/Makefile.am b/lib/csharp/Makefile.am
index be49d5e..56a8b0f 100644
--- a/lib/csharp/Makefile.am
+++ b/lib/csharp/Makefile.am
@@ -109,3 +109,7 @@
 	test \
 	coding_standards.md \
 	README.md
+
+MAINTAINERCLEANFILES = \
+	Makefile \
+	Makefile.in