Add docs for progress bars

[tiangolo]

📝 Add docs for progress bars.

[codecov-io]

Codecov Report

Merging #23 into master will increase coverage by 0.2%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master      #23     +/-   ##
=========================================
+ Coverage   97.07%   97.27%   +0.2%     
=========================================
  Files          99       99             
  Lines        1985     1985             
=========================================
+ Hits         1927     1931      +4     
+ Misses         58       54      -4

Impacted Files	Coverage Δ
...torial/test_commands/test_help/test_tutorial002.py	100% <100%> (+11.42%)	⬆️

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