Add link to GitHub issue from inline issue

Author: gsnedders

index.bs

@@ -4990,8 +4990,8 @@ Note: The minimum page size is 1 point, which is (2.54 / 72) cm as per
 1. Immediately after the next invocation of the [=run the animation frame
    callbacks=] algorithm for |document|:
 
-   Issue: This ought to be integrated into the update rendering algorithm
-   in some more explicit way.
+   Issue(w3c/webdriver-bidi#1131): This ought to be integrated into the update
+   rendering algorithm in some more explicit way.
 
   1. Let |pdf data| be the result taking UA-specific steps to generate a
      paginated representation of |document|, with the CSS [=media type=] set to