[docs/hub/spaces] mention app_file upcoming feature for static spaces

Author: julien-c

docs/hub/spaces.md

@@ -195,7 +195,7 @@ Only applicable for `streamlit` SDK. Currently available versions are :
 `0.79.0, 0.80.0, 0.81.1, 0.82.0, 0.83.0, 0.84.2, 0.85.0, 0.86.0, 0.87.0, 0.88.0, 0.89.0, 1.0.0`.
 
 **`app_file`** : _string_  
-Path to your main application file (which contains either `gradio` or `streamlit` Python code).  
+Path to your main application file (which contains either `gradio` or `streamlit` Python code, or `static` html code).
 Path is relative to the root of the repository.
 
 **`pinned`** : _boolean_