fix: improve description for configtest command

[snitin315]

What kind of change does this PR introduce?
enhancement

Did you add tests for your changes?
NA
If relevant, did you update the documentation?
Yes
Summary

improve description for configtest command.

Does this PR introduce a breaking change?
No

Other information
webpack/webpack.js.org#4450 (comment)

[codecov]

Codecov Report

Merging #2379 (a3ab330) into master (6b31614) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2379   +/-   ##
=======================================
  Coverage   70.50%   70.50%           
=======================================
  Files          47       47           
  Lines        2156     2156           
  Branches      561      561           
=======================================
  Hits         1520     1520           
  Misses        636      636           

Impacted Files	Coverage Δ
packages/configtest/src/index.ts	96.55% <ø> (ø)

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