chore: ignore .DS_Store

Two were sitting untracked in the working tree, at the root and in coreml/.
This repository is published, so anything committed here is served to every
consumer of the model.

.gitignore

@@ -0,0 +1,4 @@
+# macOS writes these into any directory Finder opens. Nothing here is edited
+# often enough for that to be noticed before a push, and this repository is
+# published — a .DS_Store committed here is served to every consumer.
+.DS_Store