correcting README

Author: mahendya1002

README.md

@@ -174,7 +174,13 @@ keytool -list -v -keystore <Your_keystore_name>`
   - Second entry should be for `CyberSource_SJC_US` certificate with alias name as CyberSource_SJC_US
 
 ## PoolingHttpClient
-5
+   PoolingHttpClient is built using the apache's PoolingHttpClientConnectionManager class. It comes with retry functionality which is very much needed in case if
+   SDK receives an I/O error/exception, when executing a request over a connection that has been closed at the server side. However there might be some cases when
+   transaction has reached server and similar or some other exception has occurred. We are considering `merchantTransactionIdentifier` as idempotent key, specially 
+   in case of auth service(`ccAuthService`). Hence if you want to use PoolingHttpClient, for auth service(`ccAuthService`) merchantTransactionIdentifier field is 
+   mandatory in the payload for both nvp and xml. The value of the merchant transaction ID must be unique for 60 days.
+   
+   To get more information related to connection pooling please refer wiki.
 
 ## Message Level Encryption
 CyberSource supports Message Level Encryption (MLE) for Simple Order API. Message level encryption conforms to the SOAP Security 1.0 specification published by the OASIS standards group.