Add .gitignore to ignore macOS system files

Change-Id: I7097ce22819daae250270119b86e7031cd3a266e
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..e43b0f9
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+.DS_Store