Add section to make clear the fact that replicator stops are async

One confusing aspect of closing a database that is being used for a replication is that you must stop a replicator, *wait for the replicator to fully stop* and only then can you close the database. Perhaps there should be a section on closing a database after the section regarding how to open one explaining this because quite a number of people have gotten tricked by this because it is not clear that the stop method is asynchronous. The linked page is for C# but this applies to all variants.