Fix description of width/height fields in render (WICG#1049)

FLEDGE.md

@@ -739,7 +739,8 @@ The output of `generateBid()` contains the following fields:
 *   bidCurrency: (optional) The currency for the bid, used for [currency-checking](#36-currency-checking).
 *   render: A dictionary describing the creative that should be rendered if this bid wins the auction. This includes:
     * url: The creative's URL.
-    * size: A dictionary containing `width` and `height` fields, describing the creative's size (see the interest group declaration above). When the ad is loaded in a fenced frame, the fenced frame's inner frame (i.e. the size visible to the ad creative) will be frozen to this size, and it will be unable to see changes to the frame size made by the embedder.
+    * width: The creative's width. This size will be matched against the declaration in the interest group and substituted into any ad size macros present in the ad creative URL. When the ad is loaded in a fenced frame, the fenced frame's inner frame (i.e. the size visible to the ad creative) will be frozen to this size, and it will be unable to see changes to the rame size made by the embedder.
+    * height: The creative's height. See elaboration in `width` above.
     
     Optionally, if you don't want to hook into interest group size declarations (e.g., if you don't want to use size macros), you can have `render` be just the URL, rather than a dictionary with `url` and `size`.
 *   adComponents: (optional) A list of up to 20 (in process of being increased to 40 starting from M122) adComponent strings from the InterestGroup's adComponents field. Each value must match one of `interestGroup`'s `adComponent`'s `renderURL` and sizes exactly. This field must not be present if `interestGroup` has no `adComponent` field. It is valid for this field not to be present even when `adComponents` is present. (See ["Ads Composed of Multiple Pieces"](#34-ads-composed-of-multiple-pieces) below.)