3.0.0: Mention that a database is still needed for account patch reviews

Change-Id: Ic55fd73a928f9086cdd1192c1ea0f1e72b509e8f
diff --git a/pages/site/releases/3.0.md b/pages/site/releases/3.0.md
index cc08204..5ee9024 100644
--- a/pages/site/releases/3.0.md
+++ b/pages/site/releases/3.0.md
@@ -15,7 +15,12 @@
 * Removal of ReviewDb
 
   The database backend for changes, accounts, groups and projects ("ReviewDb") is
-  removed and all metadata is now stored in git ("NoteDb").
+  removed and this metadata is now stored in git ("NoteDb").
+
+  A database is still needed for account patch reviews, which stores the 'reviewed'
+  flag for files in a review per user. The default backend is H2, but MySQL,
+  PostgreSQL and MariaDb are also supported. It is also possible for plugins to
+  provide another backend by implementing the `AccountPatchReviewStore` interface.
 
 ## Important Notes