Update Footnote markdown example syntax to properly display multiline footnotes in *.md pages

[timothyhull]

Why:

Issue 40887
Closes: #40887

What's being changed (if available, include any code snippets, screenshots, or gifs):

Markdown example available to copy and paste for creating multiline footnotes.

Check off the following:

• [ X ] A subject matter expert (SME) has reviewed the technical accuracy of the content in this PR. In most cases, the author can be the SME. Open source contributions may require an SME review from GitHub staff.
• [ X ] The changes in this PR meet the docs fundamentals that are required for all content.
• [ X ] All CI checks are passing and the changes look good in the review environment.

The updated syntax in the PR passes the Markdownlint check in Super Linter

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Source	Review	Production	What Changed
get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax.md	fpt ghec ghes@ 3.18 3.17 3.16 3.15 3.14	fpt ghec ghes@ 3.18 3.17 3.16 3.15 3.14

Key: fpt: Free, Pro, Team; ghec: GitHub Enterprise Cloud; ghes: GitHub Enterprise Server

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[Sharra-writes]

@timothyhull Tested it out, and you are correct! I'll get this merged.

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[timothyhull]

Thank you!