chore: add comment on PIL requirement for generate_embedding

Author: Daniel Lorch

lib/idp_common_pkg/idp_common/bedrock/client.py

@@ -720,6 +720,7 @@ def generate_embedding(
         Returns:
             List of floats representing the embedding vector
         """
+        # requires PIL
         from idp_common.image import (
             prepare_image,
             prepare_bedrock_image_attachment