added eval script and documentation

README.md

@@ -202,6 +202,41 @@ data/outputs/2023.03.01/22.13.58_train_diffusion_unet_hybrid_pusht_image
 
 7 directories, 16 files
 ```
+### 🆕 Evaluate Pre-trained Checkpoints
+Download a checkpoint from the published training log folders, such as [https://diffusion-policy.cs.columbia.edu/data/experiments/low_dim/pusht/diffusion_policy_cnn/train_0/checkpoints/epoch=0550-test_mean_score=0.969.ckpt](https://diffusion-policy.cs.columbia.edu/data/experiments/low_dim/pusht/diffusion_policy_cnn/train_0/checkpoints/epoch=0550-test_mean_score=0.969.ckpt).
+
+Run the evaluation script:
+```console
+(robodiff)[diffusion_policy]$ python eval.py --checkpoint data/0550-test_mean_score=0.969.ckpt --output_dir data/pusht_eval_output --device cuda:0
+```
+
+This will generate the following directory structure:
+```console
+(robodiff)[diffusion_policy]$ tree data/pusht_eval_output
+data/pusht_eval_output
+├── eval_log.json
+└── media
+    ├── 1fxtno84.mp4
+    ├── 224l7jqd.mp4
+    ├── 2fo4btlf.mp4
+    ├── 2in4cn7a.mp4
+    ├── 34b3o2qq.mp4
+    └── 3p7jqn32.mp4
+
+1 directory, 7 files
+```
+
+`eval_log.json` contains metrics that is logged to wandb during training:
+```console
+(robodiff)[diffusion_policy]$ cat data/pusht_eval_output/eval_log.json
+{
+  "test/mean_score": 0.9150393806777066,
+  "test/sim_max_reward_4300000": 1.0,
+  "test/sim_max_reward_4300001": 0.9872969750774386,
+...
+  "train/sim_video_1": "data/pusht_eval_output//media/2fo4btlf.mp4"
+}
+```
 
 ## 🦾 Demo, Training and Eval on a Real Robot
 Make sure your UR5 robot is running and accepting command from its network interface (emergency stop button within reach at all time), your RealSense cameras plugged in to your workstation (tested with `realsense-viewer`) and your SpaceMouse connected with the `spacenavd` daemon running (verify with `systemctl status spacenavd`).