refactor(cli): reword command help and capitalize the first characters

[bearomorphism]

[codecov[bot]]

Codecov Report

:x: Patch coverage is 97.84173% with 3 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 97.73%. Comparing base (120d514) to head (0ba30ea). :warning: Report is 885 commits behind head on master.

Files with missing lines	Patch %	Lines
commitizen/cli.py	87.50%	1 Missing :warning:
commitizen/commands/bump.py	98.03%	1 Missing :warning:
commitizen/commands/changelog.py	66.66%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1699      +/-   ##
==========================================
+ Coverage   97.33%   97.73%   +0.39%     
==========================================
  Files          42       60      +18     
  Lines        2104     2605     +501     
==========================================
+ Hits         2048     2546     +498     
- Misses         56       59       +3     

Flag	Coverage Δ
unittests	97.73% <97.84%> (+0.39%)	:arrow_up:

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