Fix PR #401 description in changelog

[MichaIng]

❓ What kind of change does this PR introduce?

• 🐞 bug fix
• 🐣 feature
• 📋 docs update
• 📋 tests/coverage improvement
• 📋 refactoring
• 💥 other

📋 What is the related issue number (starting with #)

e1a45fa

❓ What is the current behavior? (You can also link to an open issue here)

❓ What is the new behavior (if this is a feature change)?

📋 Other information:

The significant idle CPU load reduction is especially present on
non-Windows systems, having up to 100 connection handler loops per
second reduced to ~2 loops/s by default, while on Windows it is less
significant with a reduction to ~20 loops/s and with a theoretically
reduced performance when quickly repeating requests.

📋 Contribution checklist:

(If you're a first-timer, check out
this guide on making great pull requests)

• I wrote descriptive pull request text above
• I think the code is well written
• I wrote good commit messages
• I have squashed related commits together after
  the changes have been approved
• Unit tests for the changes exist
• Integration tests for the changes exist (if applicable)
• I used the same coding conventions as the rest of the project
• The new code doesn't generate linter offenses
• Documentation reflects the changes
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences

---

This change is 

[codecov]

Codecov Report

Merging #466 (7a2e25c) into master (30c91c1) will decrease coverage by 0.31%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #466      +/-   ##
==========================================
- Coverage   80.22%   79.90%   -0.32%     
==========================================
  Files          28       28              
  Lines        4395     4395              
==========================================
- Hits         3526     3512      -14     
- Misses        869      883      +14     

[MichaIng]

As the commit message check fails for forks, here the result run on my fork: https://github.com/MichaIng/cheroot/runs/4765273291

Conformance to the 7 rules of a great Git commit message:
[PASSED] Separate subject from body with a blank line
[PASSED] Limit the subject line to 50 characters
[PASSED] Capitalize the subject line
[PASSED] Do not end the subject line with a period
[PASSED] Use the imperative mood in the subject line
[PASSED] Wrap the body at 72 characters
[ NA ] Use the body to explain what and why vs. how

[webknjaz]

Thanks!