Update README.md with better preview.png example

[fuxingloh]

What kind of PR is this?:

/kind docs

[codecov]

Codecov Report

Merging #134 (effed37) into main (00c3105) will not change coverage.
The diff coverage is n/a.

❗ Current head effed37 differs from pull request most recent head 610cffc. Consider uploading reports for the commit 610cffc to get more accurate results

@@           Coverage Diff           @@
##             main     #134   +/-   ##
=======================================
  Coverage   97.33%   97.33%           
=======================================
  Files          14       14           
  Lines         488      488           
  Branches      139      139           
=======================================
  Hits          475      475           
  Misses          8        8           
  Partials        5        5           

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