[ISSUE #6133]Update the version information to 5.1.0 in README.md

[mxsm]

Make sure set the target branch to develop

What is the purpose of the change

fix #6133

Brief changelog

• Update the version information to 5.1.0 in README.md

Verifying this change

XXXX

Follow this checklist to help us incorporate your contribution quickly and easily. Notice, it would be helpful if you could finish the following 5 checklist(the last one is not necessary)before request the community to review your PR.

• Make sure there is a Github issue filed for the change (usually before you start working on it). Trivial changes like typos do not require a Github issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue.
• Format the pull request title like [ISSUE #123] Fix UnknownException when host config not exist. Each commit in the pull request should have a meaningful subject line and body.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test(over 80% coverage) to verify your logic correction, more mock a little better when cross module dependency exist. If the new feature or significant change is committed, please remember to add integration-test in test module.
• Run mvn -B clean apache-rat:check findbugs:findbugs checkstyle:checkstyle to make sure basic checks pass. Run mvn clean install -DskipITs to make sure unit-test pass. Run mvn clean test-compile failsafe:integration-test to make sure integration-test pass.
• If this contribution is large, please file an Apache Individual Contributor License Agreement.

[codecov-commenter]

Codecov Report

Merging #6134 (0658277) into develop (7049527) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             develop    #6134   +/-   ##
==========================================
  Coverage      43.24%   43.24%           
- Complexity      8845     8852    +7     
==========================================
  Files           1094     1094           
  Lines          77137    77137           
  Branches       10057    10057           
==========================================
  Hits           33355    33355           
- Misses         39613    39618    +5     
+ Partials        4169     4164    -5     

Impacted Files	Coverage Δ
...ketmq/proxy/grpc/v2/channel/GrpcClientChannel.java	49.07% <0.00%> (-2.78%)	⬇️
...he/rocketmq/controller/impl/DLedgerController.java	66.49% <0.00%> (-2.62%)	⬇️
...he/rocketmq/broker/controller/ReplicasManager.java	44.40% <0.00%> (-2.62%)	⬇️
.../apache/rocketmq/controller/ControllerManager.java	71.87% <0.00%> (-2.09%)	⬇️
...e/rocketmq/store/ha/autoswitch/EpochFileCache.java	77.08% <0.00%> (-1.39%)	⬇️
...he/rocketmq/client/impl/consumer/ProcessQueue.java	61.23% <0.00%> (-0.89%)	⬇️
...ent/impl/consumer/DefaultLitePullConsumerImpl.java	68.17% <0.00%> (-0.47%)	⬇️
...apache/rocketmq/store/timer/TimerMessageStore.java	54.15% <0.00%> (-0.10%)	⬇️
...ava/org/apache/rocketmq/filter/util/BitsArray.java	59.82% <0.00%> (ø)
...main/java/org/apache/rocketmq/store/CommitLog.java	65.13% <0.00%> (+0.10%)	⬆️
... and 7 more

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[francisoliverlee]

4.9.X和5.X的版本在组件上差异还是比较大， 把4.9.X和5.X的 README 都保留吧

[drpmma]

LGTM