message: Add "Update rendered link" to RFC merge procedure
diff: @@ -65,5 +65,12 @@ flavor (and change the team):
  To track further discussion, subscribe to the tracking issue here: rust-lang/rust#41517
  ```
  +### Step 4: Update the rendered link
  +
  +Update the rendered link in the first post of the PR to the permanent home under
  +`https://github.com/rust-lang/rfcs/blob/master/text/`.
  +
  +(This way future visitors can open it easily after the PR branch is deleted.)
  +
  ### That's it, you're done!
  