docs: removing customization file contradiction

[chr15murray]

Description

Customising via the configuration file is clearly possible when using yaml files since you show an example for this. This PR updates the doc to remove the warning that states this is not possible. Given that yaml was the only missing file type in the original warning it seems safe to remove it completely.

Checklist

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

Expected behavior

N/A - Docs updated only

Steps to Test This Pull Request

N/A - Docs updated only

Additional context

N/A - Docs updated only

[codecov]

Codecov Report

Merging #471 (293cc84) into master (308de9c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #471   +/-   ##
=======================================
  Coverage   98.04%   98.04%           
=======================================
  Files          39       39           
  Lines        1431     1431           
=======================================
  Hits         1403     1403           
  Misses         28       28           

Flag	Coverage Δ
unittests	98.04% <ø> (ø)

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[Lee-W]

Thanks for fixing the doc!