docs: clarify file extension for module type

[danielrhodeswarp]

Description

I have clarified this point which was, at least for me, a bit of a "huh?" moment:
"If you use mjs version of the code,..." when the code snippets prior are simply labelled CJS and ESM.

So I suggest a change to:
"If you use the ESM version of the code,..."

Validation

Check, in the browser, the first page of "Introduction to Node.js". The change is just after the first code snippet.

Related Issues

Check List

• I have read the Contributing Guidelines and made commit messages that follow the guideline.
• I have run pnpm format to ensure the code follows the style guide.
• I have run pnpm test to check if all tests are passing.
• I have run pnpm build to check if the website builds without errors.
• I've covered new added functionality with unit tests if necessary.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
nodejs-org	Ready	Preview	Mar 5, 2026 2:50pm

[github-actions]

👋 Codeowner Review Request

The following codeowners have been identified for the changed files:

Team reviewers: @nodejs/nodejs-website

Please review the changes when you have a chance. Thank you! 🙏

[aymen94]

LGTM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.10%. Comparing base (252f977) to head (56ff779).
⚠️ Report is 7 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8697      +/-   ##
==========================================
+ Coverage   75.05%   75.10%   +0.04%     
==========================================
  Files         104      104              
  Lines        9161     9161              
  Branches      316      315       -1     
==========================================
+ Hits         6876     6880       +4     
+ Misses       2283     2279       -4     
  Partials        2        2              

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[github-actions]

Lighthouse Results

URL	Performance	Accessibility	Best Practices	SEO	Report
/en	🟢 99	🟢 93	🟢 100	🟢 100	🔗
/en/about	🟢 100	🟢 94	🟢 100	🟠 88	🔗
/en/about/previous-releases	🟢 97	🟢 97	🟢 100	🟢 100	🔗
/en/download	🟢 99	🟢 96	🟠 81	🟢 100	🔗
/en/download/archive/current	🟢 100	🟢 97	🟢 100	🟢 100	🔗
/en/blog	🟢 100	🟢 97	🟢 96	🟢 100	🔗

[mikeesto]

LGTM, thanks