add global.json files for C#
diff --git a/src/csharp/global.json b/src/csharp/global.json
new file mode 100644
index 0000000..e4b797e
--- /dev/null
+++ b/src/csharp/global.json
@@ -0,0 +1,5 @@
+{
+  "sdk": {
+    "version": "1.0.0"
+  }
+}