Update HISTORY for db_bench changes (#9759)

Summary:
These should have been part of the original PRs that changed db_bench, but I forgot to do that.
The PRs are:
* https://github.com/facebook/rocksdb/pull/9740
* https://github.com/facebook/rocksdb/pull/9733

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9759

Test Plan: No test needed.

Reviewed By: jay-zhuang

Differential Revision: D35159553

Pulled By: mdcallag

fbshipit-source-id: b44d075527309ee0bd4c5a92e5dd94ebf72f363e

HISTORY.md

@@ -4,6 +4,9 @@
 * Fixed a race condition when 2PC is disabled and WAL tracking in the MANIFEST is enabled. The race condition is between two background flush threads trying to install flush results, causing a WAL deletion not tracked in the MANIFEST. A future DB open may fail.
 * Fixed a heap use-after-free race with DropColumnFamily.
 * Fixed a bug that `rocksdb.read.block.compaction.micros` cannot track compaction stats (#9722).
+### New Features
+* For db_bench when --seed=0 or --seed is not set then it uses the current time as the seed value. Previously it used the value 1000.
+* For db_bench when --benchmark lists multiple tests and each test uses a seed for a RNG then the seeds across tests will no longer be repeated.
 
 ## 7.1.0 (03/23/2022)
 ### New Features