docs: remind user again change the data path

[bwanglzu]

users might just copy-paste the code without noticing, here we remind again in comments.

[codecov]

Codecov Report

Merging #158 (cf11603) into main (f6ba40d) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #158   +/-   ##
=======================================
  Coverage   84.90%   84.90%           
=======================================
  Files          24       24           
  Lines        1166     1166           
=======================================
  Hits          990      990           
  Misses        176      176           

Flag	Coverage Δ
finetuner	84.90% <100.00%> (ø)

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Impacted Files	Coverage Δ
finetuner/__init__.py	70.37% <100.00%> (ø)

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[tadejsv]

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