Update README.md

[jamieliu1023]

What type of PR is this?

• bug
• feature
• enhancement

What does this PR do?

Updated the link to the forum in README.

Which issue(s)/PR(s) this PR relates to?

None.

Special notes for your reviewer, ex. impact of this fix, etc:

The Discussions tab has just been enabled.

Additional context:

Checklist：

• Documentation affected （Please add the label if documentation needs to be modified.)
• Incompatible （If it is incompatible, please describe it and add corresponding label.）
• Need to cherry-pick （If need to cherry-pick to some branches, please label the destination version(s).)
• Performance impacted: Consumes more CPU/Memory

Release notes：

Please confirm whether to reflect in release notes and how to describe:

                                                            `

[CLAassistant]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

Merging #3371 (036265c) into master (e981c3f) will decrease coverage by 0.65%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3371      +/-   ##
==========================================
- Coverage   85.23%   84.58%   -0.66%     
==========================================
  Files        1276     1276              
  Lines      119001   118998       -3     
==========================================
- Hits       101436   100649     -787     
- Misses      17565    18349     +784     

Impacted Files	Coverage Δ
src/meta/processors/job/AdminJobProcessor.h	0.00% <0.00%> (-100.00%)	⬇️
src/meta/processors/job/FlushJobExecutor.cpp	0.00% <0.00%> (-100.00%)	⬇️
src/meta/processors/job/ReportTaskProcessor.h	0.00% <0.00%> (-100.00%)	⬇️
src/meta/processors/job/CompactJobExecutor.cpp	0.00% <0.00%> (-100.00%)	⬇️
src/meta/processors/job/RebuildTagJobExecutor.cpp	0.00% <0.00%> (-100.00%)	⬇️
src/meta/processors/job/RebuildEdgeJobExecutor.cpp	0.00% <0.00%> (-100.00%)	⬇️
src/meta/processors/parts/CreateSpaceAsProcessor.h	0.00% <0.00%> (-100.00%)	⬇️
.../meta/processors/job/ListTagIndexStatusProcessor.h	0.00% <0.00%> (-100.00%)	⬇️
...meta/processors/job/ListEdgeIndexStatusProcessor.h	0.00% <0.00%> (-100.00%)	⬇️
src/meta/processors/job/ReportTaskProcessor.cpp	0.00% <0.00%> (-85.72%)	⬇️
... and 56 more

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[SuperYoko]

Maybe it is not proper to put this Discussions link in Getting help

[darionyaphet]

Maybe it is not proper to put this Discussions link in Getting help

otherwise no one can find it