[AdTagging] Link filter lists in readme

Change-Id: I37844a17016f490c3e96afdffe1bf9c0c529b1b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3265494
Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Commit-Queue: John Delaney <johnidel@chromium.org>
Cr-Commit-Position: refs/heads/main@{#947062}

docs/ad_tagging.md

@@ -10,7 +10,11 @@ behavior](https://support.google.com/webtools/answer/7347327).
 The ad detection infrastructure is called Ad Tagging. Ad Tagging works by
 matching resource requests against a filter list (see how the list is
 [generated](https://chromium.googlesource.com/chromium/src.git/+/main/components/subresource_filter/FILTER_LIST_GENERATION.md))
-to determine if they’re ad requests. Any requests matching the filter are tagged
+to determine if they’re ad requests.
+
+The current filter list and historical versions can be found [here](https://github.com/chromium/chromium-ads-detection).
+
+Any requests matching the filter are tagged
 as ads. Further, requests (and some DOM elements such as iframes) made on behalf
 of previously tagged scripts are also tagged as ads by the
 [AdTracker](https://cs.chromium.org/chromium/src/third_party/blink/renderer/core/frame/ad_tracker.h). An