update mirror clone help

[nexustar]

What problem does this PR solve?

• close Add an example in -h for tiup mirror clone for multiple versions  #1980

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release notes:

NONE

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• srstack

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[codecov-commenter]

Codecov Report

Merging #2009 (a715081) into master (25b38a0) will decrease coverage by 1.28%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2009      +/-   ##
==========================================
- Coverage   52.60%   51.32%   -1.28%     
==========================================
  Files         308      308              
  Lines       35877    35878       +1     
==========================================
- Hits        18873    18413     -460     
- Misses      14785    15260     +475     
+ Partials     2219     2205      -14     

Flag	Coverage Δ
cluster	39.55% <ø> (-1.75%)	⬇️
dm	24.15% <ø> (ø)
playground	12.96% <ø> (ø)
tiup	14.27% <100.00%> (+<0.01%)	⬆️
unittest	20.82% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/mirror.go	44.63% <100.00%> (+0.07%)	⬆️
pkg/cluster/template/config/ngmonitoring.go	0.00% <0.00%> (-76.47%)	⬇️
pkg/cluster/api/cdcapi.go	0.00% <0.00%> (-54.12%)	⬇️
pkg/cluster/template/scripts/cdc.go	55.74% <0.00%> (-24.59%)	⬇️
pkg/cluster/operation/scale_in.go	32.88% <0.00%> (-21.58%)	⬇️
pkg/cluster/spec/cdc.go	39.16% <0.00%> (-21.08%)	⬇️
pkg/cluster/task/update_meta.go	69.89% <0.00%> (-15.05%)	⬇️
pkg/cluster/spec/monitoring.go	66.25% <0.00%> (-9.29%)	⬇️
pkg/cluster/task/task.go	64.81% <0.00%> (-8.33%)	⬇️
pkg/tidbver/tidbver.go	91.67% <0.00%> (-8.33%)	⬇️
... and 21 more

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[srstack]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: a715081