Add note about replica set requirements

Author: alcaeus

examples/changestream.php

@@ -23,6 +23,7 @@ function toJSON(object $document): string
     return toRelaxedExtendedJSON(fromPHP($document));
 }
 
+// Change streams require a replica set or sharded cluster
 $client = new Client(getenv('MONGODB_URI') ?: 'mongodb://127.0.0.1/');
 
 $collection = $client->test->coll;

examples/with_transaction.php

@@ -21,6 +21,7 @@ function toJSON(object $document): string
     return toRelaxedExtendedJSON(fromPHP($document));
 }
 
+// Transactions require a replica set (MongoDB >= 4.0) or sharded cluster (MongoDB >= 4.2)
 $client = new Client(getenv('MONGODB_URI') ?: 'mongodb://127.0.0.1/');
 
 $collection = $client->test->coll;