update readme for v6.8 (#48)

* update readme for v6.8

* Update README.md

Author: hhakimi53

README.md

@@ -18,6 +18,12 @@ The OSX binary was compiled with Xcode 7.2 on OSX 10.11.
 The source code is available in the [VoltDB Github repository]
 (https://github.com/VoltDB/voltdb-client-cpp). 
 
+New Features in V6.8
+==================
+- Update backpressure notification to notify when backpressure on client transitions from on to off
+- Fix handling of pending connection logic where client gets disconnected and tries to reconnect, if socket timeout is longer than 10 seconds, it can potentially crash the client
+- Update setaffinity logic to not drop the set affinity request in case of backpresure with client configured with enable abandon set to true.
+
 New Features in V6.0
 ==================