add release note file

CHANGES.md

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+
+# Table of Contents
+
+- [0.9.8-rc01](#0.9.8-rc01)
+
+## 0.9.8-rc01
+
+* Fix bug that time unit is not listed in grpc timeout options.
+https://github.com/apache/incubator-brpc/pull/1036
+* Fix heap overflow in simple_data_pool
+https://github.com/apache/incubator-brpc/pull/1056
+* Make args of redis protocol be StringPiece
+https://github.com/apache/incubator-brpc/pull/1128
+* Support the length of redis args could be zero
+https://github.com/apache/incubator-brpc/pull/1128
+* Optimize code in timer_thread
+https://github.com/apache/incubator-brpc/pull/1137/files
+* Fix a narrowing warning on aarch64
+https://github.com/apache/incubator-brpc/commit/87f149c464ea0322a5b59d040bb80e7847f365be
+* Make pthread_atfork not registered in child process
+https://github.com/apache/incubator-brpc/commit/2f8fc37d52c2a02ee6f348aaa52c7ded4a4844c3
+* Rename LOG_NONE which conflicts with a name in mysql
+https://github.com/apache/incubator-brpc/commit/e3840c18cdd9e1ff81f8280b96ac14869007a122
+* Fix several warnings under MAC
+https://github.com/apache/incubator-brpc/commit/f8c188a7a5186c2d43a20735ad175a32b39788a3
+* Ignore ELIMIT for circuit breaker
+https://github.com/apache/incubator-brpc/pull/1005
+* limit minimum value of max_concurrency for auto_cl
+https://github.com/apache/incubator-brpc/pull/1003