Update to "Styling text" section

[LRANUL]

• Added writing superscript syntax on GitHub markdowns for inline text to be displayed as superscript
• Added writing subscript syntax on GitHub markdowns for inline text to be displayed as subscript

Reference Issue: #17618

Why:

For improving GitHub's user experience by allowing scientistic communities to use notations as in-text, this allows easier interactions compared to images.

Closes Issue #17618

What's being changed:

Changes will be made to Styling text section of the page, new addition will improve the overall GitHub experience by helping scientistic communities to use scientific and mathematical notations effortlessly.
e.g.

1. The chemical notation of water could be interpreted as H₂O by writing as H<sub>2</sub>O
2. The mathematical equation of Pythagorean could be interpreted as a²+ b² = c² by writing as a<sup>2</sup>+ b<sup>2</sup> = c<sup>2</sup>

Updates

• Added writing superscript syntax on GitHub markdowns for inline text to be displayed as superscript
• Added writing subscript syntax on GitHub markdowns for inline text to be displayed as subscript

Notes

This information will support communities to use majority of notions used in the science as intext writing compared to images uploaded, for a complete coverage GitHub's internal features will need to improved in the future as the system is upgraded.

Screenshot

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Writer impact (This section is for GitHub staff members only):

• This pull request impacts the contribution experience
  • I have added the 'writer impact' label
  • I have added a description and/or a video demo of the changes below (e.g. a "before and after video")

[github-actions]

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Content directory changes

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Source	Preview	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@ 3.5 3.4 3.3 3.2 3.1 ghae	fpt ghec ghes@ 3.5 3.4 3.3 3.2 3.1 ghae

[ramyaparimi]

@LRANUL
Thanks so much for opening a PR! I'll get this triaged for review ⚡

[skedwards88]

Thanks for this addition! We'll merge this down for you.

[github-actions]

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