docs(readme): update CIVITAI Model URL

[Anime4000]

Hi, this is simple README.md edit just to update CIVITAI Link.

The old link no longer works for quite sometime, and this small README.md update use correct CIVITAI Link.

CIVITAI has tag for so-vits-svc-fork which is contain 15 model compared with just so-vits-svc (10 model)

Thank You

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 19.25%. Comparing base (55bbf0a) to head (93503a6).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1250   +/-   ##
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  Coverage   19.25%   19.25%           
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  Files          39       39           
  Lines        3496     3496           
  Branches      610      610           
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  Hits          673      673           
- Misses       2803     2804    +1     
+ Partials       20       19    -1     

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