docs: clarify component naming for markdown import

[jackrabbit128]

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

As someone who barely knows any Javascript, I did not succeed in importing a markdown document from an mdx one. Adding the proposed clarification would have saved me some time and frustration.

Test Plan

It is a documentation change. I verified it using github's markdown preview.

Test links

Deploy preview: https://deploy-preview-10545--docusaurus-2.netlify.app/docs/markdown-features/react/#importing-markdown

Related issues/PRs

Fixes #10542

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

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/docs/installation	🟠 51	🟢 97	🟢 100	🟢 100	Report
/docs/category/getting-started	🟠 73	🟢 100	🟢 100	🟠 86	Report
/blog	🟠 60	🟢 96	🟢 100	🟠 86	Report
/blog/preparing-your-site-for-docusaurus-v3	🔴 47	🟢 92	🟢 100	🟢 100	Report
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/blog/tags	🟠 75	🟢 100	🟢 100	🟠 86	Report

[Josh-Cena]

👍 Thanks!