NEWS: add v3.2.1
Highlights some important bug fixes + user facing
changes in debugging metrics.
+etcd v3.2.1 (2017-06-23)
+- fix backend database index corruption issue on restore
+- fix gRPC gateway Txn marshaling issue
+- fix backend database size debugging metrics
+
etcd v3.2.0 (2017-06-09)
- improved backend read concurrency
- embedded etcd
