[css-fonts-4] Add suggested user prompting to make local fonts available #4497

Author: svgeesus

css-fonts-4/Overview.bs

@@ -8011,8 +8011,9 @@ User Agents may choose to make all installed fonts available
 for language support and design integrity reasons, 
 or may choose to make some fonts unavailable for privacy reasons. 
 In addition, User Agents may have additional facilities for fine-tuning this balance, 
-such as interfaces to allow users to explicitly make 
-certain fonts available or unavailable. 
+such as interfaces which prompt users to explicitly make 
+certain requested fonts available or unavailable
+(perhaps on a per-site basis). 
 Different User Agents, even running on the same Operating System, 
 are expected to strike different balances here.