[ISSUE #6774]Update README.md rocketmq version to 5.1.1

[mxsm]

Which Issue(s) This PR Fixes

Fixes #6774

Brief Description

• Update README.md rocketmq version to 5.1.1

How Did You Test This Change?

[codecov-commenter]

Codecov Report

Merging #6775 (5e5e682) into develop (9dfd4a9) will increase coverage by 0.10%.
The diff coverage is 100.00%.

@@              Coverage Diff              @@
##             develop    #6775      +/-   ##
=============================================
+ Coverage      42.84%   42.95%   +0.10%     
- Complexity      8976     8987      +11     
=============================================
  Files           1108     1104       -4     
  Lines          78444    78380      -64     
  Branches       10212    10203       -9     
=============================================
+ Hits           33607    33665      +58     
+ Misses         40617    40499     -118     
+ Partials        4220     4216       -4     

Impacted Files	Coverage Δ
...client/consumer/store/RemoteBrokerOffsetStore.java	68.75% <100.00%> (-0.28%)	⬇️

... and 17 files with indirect coverage changes

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