README.md in dockly-1.5.0 vs README.md in dockly-1.5.1

@@ -91,9 +91,13 @@
     - description: where the build cache files are stored locally; this should be able to be removed easily since they all exist in S3 as well
 - `use_latest`
     - required: `false`
     - default: `false`
     - description: when using S3, will insert the S3 object tagged as latest in your "s3://s3_bucket/s3_object_prefix" before running the build command to quicken build times
+- `keep_old_files`
+    - required: `false`
+    - default: `false`
+    - description: if this option is false when using docker, it will overwrite files that already exist in `output_dir`
 
 `docker`
 --------
 
 The `docker` DSL is used to define Docker containers. It has the following attributes: