ChangeInfo: Document assignee and hashtags fields

Change-Id: I6ad7fac8209fb101d69cb29f5f89dc25279ecdf8
Signed-off-by: Edwin Kempin <ekempin@google.com>
diff --git a/Documentation/rest-api-changes.txt b/Documentation/rest-api-changes.txt
index bf7bae4..cb161af 100644
--- a/Documentation/rest-api-changes.txt
+++ b/Documentation/rest-api-changes.txt
@@ -5636,6 +5636,12 @@
 The name of the target branch. +
 The `refs/heads/` prefix is omitted.
 |`topic`              |optional|The topic to which this change belongs.
+|`assignee`           |optional|
+The assignee of the change as an link:rest-api-accounts.html#account-info[
+AccountInfo] entity.
+|`hashtags`           |optional|
+List of hashtags that are set on the change (only populated when NoteDb
+is enabled).
 |`change_id`          ||The Change-Id of the change.
 |`subject`            ||
 The subject of the change (header line of the commit message).