CHANGELOG: document doc imports

Change-Id: I81fa11c278ce5370906ad3b057e79dca838b0f43
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/425183
Reviewed-by: Kevin Moore <kevmoo@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>
Commit-Queue: Kevin Moore <kevmoo@google.com>

Author: srawlins

CHANGELOG.md

@@ -68,6 +68,11 @@ var listWithNullAwareElements = [
 
 #### Analyzer
 
+- The analyzer now supports "doc imports," a new comment-based syntax which
+  enables external elements to be referenced in documentation comments without
+  actually importing them. See [the
+  documentation](https://dart.dev/tools/doc-comments/references#doc-imports)
+  for details.
 - Code completion is improved to offer more valid suggestions. In particular,
   the suggestions are improved when completing text in a comment reference on a
   documentation comment for an extension, a typedef, or a directive (an import,