doc: make the chart installation doc easier to understand.

[jwcesign]

What type of PR is this?
/kind documentation

What this PR does / why we need it:
Paragraph segmentation blurs, making it clearer.

Which issue(s) this PR fixes:
Fixes #none

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[jwcesign]

/cc @calvin0327

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (bf1098b) 52.80% compared to head (b867465) 52.01%.
Report is 12 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4300      +/-   ##
==========================================
- Coverage   52.80%   52.01%   -0.80%     
==========================================
  Files         240      242       +2     
  Lines       23624    23993     +369     
==========================================
+ Hits        12474    12479       +5     
- Misses      10471    10833     +362     
- Partials      679      681       +2     

Flag	Coverage Δ
unittests	52.01% <ø> (-0.80%)	⬇️

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[chaosi-zju]

/lgtm

[jwcesign]

/cc @RainbowMango

[RainbowMango]

/approve
Thanks.

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: RainbowMango

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[chaunceyjiang]

/lgtm