Add some documents for JTubeSpeech

[sw005320]

What?

Adding detailed instructions for JTubeSpeech data.

Why?

There is some missing information.

See also

#5662

[sw005320]

@Takaaki-Saeki and @vebmaylrie, I'm not very sure about how to get the single-speaker partition.
Can you give me more information?

FYI, https://github.com/sarulab-speech/jtubespeech?tab=readme-ov-file#step5-asv-speaker-variation-scoring seems to be incomplete.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.61%. Comparing base (fa822d5) to head (173a209).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5663      +/-   ##
==========================================
+ Coverage   72.21%   76.61%   +4.39%     
==========================================
  Files         760      761       +1     
  Lines       69840    69880      +40     
==========================================
+ Hits        50435    53536    +3101     
+ Misses      19405    16344    -3061     

Flag	Coverage Δ
test_configuration_espnet2	?
test_integration_espnet1	62.92% <ø> (ø)
test_integration_espnet2	48.84% <ø> (?)
test_integration_espnetez	27.98% <ø> (ø)
test_python_espnet1	18.20% <ø> (ø)
test_python_espnet2	52.41% <ø> (ø)
test_python_espnetez	13.95% <ø> (ø)
test_utils	20.91% <ø> (ø)

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.