add input image requirement in README

README.md

@@ -306,6 +306,7 @@ Download PhotoMaker model file (in safetensor format) [here](https://huggingface
 
 - Specify the PhotoMaker model path using the `--stacked-id-embd-dir PATH` parameter. 
 - Specify the input images path using the `--input-id-images-dir PATH` parameter. 
+  - input images **must** have the same width and height for preprocessing (to be improved)
 
 In prompt, make sure you have a class word followed by the trigger word ```"img"``` (hard-coded for now). The class word could be one of ```"man, woman, girl, boy"```. If input ID images contain asian faces, add ```Asian``` before the class
 word.