Update README.md

Author: 2color

docs/core-api/README.md

@@ -19,7 +19,7 @@ It is broken up into the following sections:
 * [KEY.md](KEY.md)
 * [MISCELLANEOUS.md](MISCELLANEOUS.md)
 * [NAME.md](NAME.md)
-* [OBJECT.md](OBJECT.md)
+* [OBJECT.md](OBJECT.md) (Now deprecated and should be avoided. Use the [DAG API](DAG.md) instead)
 * [PIN.md](PIN.md)
 * [PUBSUB.md](PUBSUB.md)
 * [REFS.md](REFS.md)