add editorconfig for C#
diff --git a/src/csharp/.editorconfig b/src/csharp/.editorconfig
new file mode 100644
index 0000000..7bc2bcc
--- /dev/null
+++ b/src/csharp/.editorconfig
@@ -0,0 +1,7 @@
+root = true
+[**]
+end_of_line = LF
+indent_style = space
+indent_size = 4
+insert_final_newline = true
+tab_width = 4