Update yolov5.ipynb (#3462)

Changing image name to lowercase since it errors out on `invalid reference format: repository name must be lowercase` during build and push

training/distributed_training/pytorch/data_parallel/yolov5/yolov5.ipynb

@@ -104,7 +104,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "image = \"YOLOv5-smdataparallel-sagemaker\"  # use any image name you want\n",
+    "image = \"yolov5-smdataparallel-sagemaker\"  # use any image name you want, as long as it is all lower case\n",
     "tag = \"pt1.10.2\"  # use any tag name you want"
    ]
   },