Update upload docstring (#848)

pynecone/components/forms/upload.py

@@ -18,7 +18,9 @@ class Upload(Component):
 
     tag = "ReactDropzone"
 
-    # The list of accepted file types.
+    # The list of accepted file types. This should be a dictionary of MIME types as keys and array of file formats as
+    # values.
+    # supported MIME types: https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/MIME_types/Common_types
     accept: Var[Optional[Dict[str, List]]]
 
     # Whether the dropzone is disabled.