docs: add warning that certain rule customizations may result in false negatives

[hudlow]

PR summary

Add cautionary note to ruleset customization docs that disabling some rules may result in false negatives for other rules.

PR Checklist

General checklist

Please make sure that your PR fulfills the following requirements:

• [x] The commit message follows the Angular Commit Message Guidelines.
• [ ] ~Tests for the changes have been added (for bug fixes / features)~
• [ ] ~Docs have been added / updated (for bug fixes / features)~
• [ ] ~Dependencies have been updated as needed~
• [ ] ~.secrets.baseline updated as needed?~

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[ibm-devx-sdk]

:tada: This PR is included in version 1.19.0 :tada:

The release is available on npm package (@latest dist-tag)

Your semantic-release bot :package::rocket:

[ibm-devx-sdk]

:tada: This PR is included in version 1.20.0 :tada:

The release is available on npm package (@latest dist-tag)

Your semantic-release bot :package::rocket: