Update BT docstring

[pilot7747]

Artifacts from previous docs format.

Checklist

• [x] I have read the CONTRIBUTING document
• [x] 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
• [x] My change requires a change to the documentation
• [x] I have updated the documentation accordingly
• [x] I have added tests to cover my changes
• [x] 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 :white_check_mark:

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

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Additional details and impacted files

```diff @@ 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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