update readme

README.md

@@ -51,7 +51,7 @@ display(image)
 
 Use a positive `seed` for reproducible results.  Higher values for `log2_supercondition_factor` result in better agreement with the text but a narrower variety of generated images.
 
-If the model is being used interactively (e.g. in a notebook) `generate_image_stream` can be used to generate a stream of images as it the model is decoding.  The detokenizer adds a slight delay for each intermediate image.
+If the model is being used interactively (e.g. in a notebook) `generate_image_stream` can be used to generate a stream of images as it the model is decoding.  The detokenizer adds a slight delay for each intermediate image.  Setting `log2_mid_count` to 3 results in a total of `2 ** 3 = 8` generated images.  The only valid values for `log2_mid_count` are 0, 1, 2, 3, 4.
 
 ```python
 image_stream = model.generate_image_stream(