minor fix in controlnet flax example (huggingface#2986)

* fix the error when push_to_hub but not log validation

* contronet_from_pt & controlnet_revision

* add intermediate checkpointing to the guide

Author: yiyixuxu

examples/controlnet/README.md

@@ -326,6 +326,7 @@ If you want to use Weights and Biases logging, you should also install `wandb` n
 pip install wandb
 ```
 
+
 Now let's downloading two conditioning images that we will use to run validation during the training in order to track our progress
 
 ```

examples/controlnet/train_controlnet_flax.py

@@ -216,6 +216,17 @@ def parse_args():
         action="store_true",
         help="Load the pretrained model from a PyTorch checkpoint.",
     )
+    parser.add_argument(
+        "--controlnet_revision",
+        type=str,
+        default=None,
+        help="Revision of controlnet model identifier from huggingface.co/models.",
+    )
+    parser.add_argument(
+        "--controlnet_from_pt",
+        action="store_true",
+        help="Load the controlnet model from a PyTorch checkpoint.",
+    )
     parser.add_argument(
         "--profile_steps",
         type=int,