Update thread-request box to be less leading and more helpful

Author: clarfonthey

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,7 +1,7 @@
 <!-- Thank you for trying to improve Rust through the RFC process! -->
 <!-- Please add a short summary of your RFC below -->
 
-> [!IMPORTANT]  
-> When responding to RFCs, try to use inline review comments (it is possible to leave an inline review comment for the entire file at the top) instead of direct comments for normal comments and keep normal comments for procedural matters like starting FCPs.
+> [!IMPORTANT]
+> Since RFCs involve many conversations at once that can be difficult to follow, please use review comment threads on the text changes instead of direct comments on the RFC.
 >
-> This keeps the discussion more organized.
+> If you don't have a particular section of the RFC to comment on, you can click on the "Comment on this file" button on the top-right corner of the diff, to the right of the "Viewed" checkbox. This will create a separate thread even if others have commented on the file too.