docs(contributing): do not request modifications to changelog

[woile]

Description

Update contribution guidelines

Checklist

• Add test cases to all the changes you introduce
• Run ./script/format and ./script/test locally to ensure this change passes linter check and test
• Test the changes on the local machine manually
• Update the documentation for the changes

[codecov]

Codecov Report

Merging #409 (33c3c49) into master (184c439) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #409   +/-   ##
=======================================
  Coverage   97.90%   97.90%           
=======================================
  Files          39       39           
  Lines        1381     1381           
=======================================
  Hits         1352     1352           
  Misses         29       29           

Flag	Coverage Δ
unittests	97.90% <100.00%> (ø)

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Impacted Files	Coverage Δ
commitizen/commands/init.py	91.66% <ø> (ø)
commitizen/__version__.py	100.00% <100.00%> (ø)

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