Update multi-threaded mode defaults in features.html

h2/src/docsrc/html/features.html

@@ -858,10 +858,14 @@ This database synchronizes access to the same connection, but other databases ma
 To get higher concurrency, you need to use multiple connections.
 </p>
 <p>
-By default, requests to the same database are synchronized.
-That means an application can use multiple threads that access the same database
-at the same time, however if one thread executes a long running query, the other threads need to wait.
-To enable concurrent database usage, see the setting <code>MULTI_THREADED</code>.
+An application can use multiple threads that access the same database at the same time.
+With default MVStore engine threads that use different connections can use the database concurrently.
+With PageStore engine requests to the same database are synchronized,
+that means that if one thread executes a long running query, the other threads need to wait.
+Concurrent database usage may be enabled for PageStore or disabled for MVStore
+with <code>MULTI_THREADED</code> setting.
+Note that multi-threaded mode for PageStore engine is not tested well and has some issues;
+it should be used with caution.
 </p>
 
 <h3>Locking, Lock-Timeout, Deadlocks</h3>