tweak meta fields for transactions

Author: kay-kim

source/core/transactions.txt

@@ -11,8 +11,8 @@ Transactions
    :class: twocols
 
 .. meta::
-   :description: transactions, multi-document transactions, multi-statement transactions
-   :keywords: transactions, multi-document transactions, multi-statement transactions
+   :description: MongoDB transactions, MongoDB multi-document transactions, MongoDB multi-statement transactions, java transaction examples, python transaction examples, node transaction examples, php transaction examples, scala transaction examples, csharp transaction examples, perl transaction examples, ruby transaction examples
+   :keywords: MongoDB, transactions, MongoDB multi-document transactions, MongoDB multi-statement transactions, java transaction examples, python transaction examples, node transaction examples, php transaction examples, scala transaction examples, csharp transaction examples, perl transaction examples, ruby transaction examples
 
 .. versionadded:: 4.0