add README

ppgan/metric/README.md

@@ -6,5 +6,5 @@ To compute the FID score between two datasets, where images of each dataset are
 
 Download [InceptionV3](https://paddlegan.bj.bcebos.com/InceptionV3.pdparams) inference model, and then run
 ```
-python test_fid_score.py --image_data_path1 /path/to/dataset1 --image_data_path2 /path/to/dataset2 --inference_model /path/to/InceptionV3/inference_moel
+python test_fid_score.py --image_data_path1 /path/to/dataset1 --image_data_path2 /path/to/dataset2 --inference_model /path/to/InceptionV3/inference_model
 ```