Update BT docstring

[pilot7747]

Artifacts from previous docs format.

Checklist

• I have read the CONTRIBUTING document
• I hereby agree to the terms of either individual CLA available at: https://toloka.ai/legal/cla_individual or corporate CLA available at: https://toloka.ai/legal/cla_corporate, whichever is applicable to me, as it pertains to direct contributions to crowd-kit only
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

[dustalov]

Please wait for the tests and then merge.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.98%. Comparing base (e67d3a7) to head (21d5025).

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #119   +/-   ##
=======================================
  Coverage   92.98%   92.98%           
=======================================
  Files          47       47           
  Lines        2251     2251           
=======================================
  Hits         2093     2093           
  Misses        158      158           

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