Add introductory note for new open source contributors

[AyoubMeftah02]

Added a note indicating the content is for newcomers to open source.

Please confirm this pull request meets the following requirements:

• I followed the contributing guidelines: https://github.com/github/explore/blob/main/CONTRIBUTING.md.
• This change is not self-promotion.

Which change are you proposing?

• Suggesting edits to an existing topic or collection
• Curating a new topic or collection
• Something that does not neatly fit into the binary options above

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Editing an existing topic or collection

I'm suggesting these edits to an existing topic or collection:

• Image (and my file is *.png, square, dimensions 288x288, size <= 75 kB)
• Content (and my changes are in index.md)

Please replace this line with an explanation of why you think these changes should be made.

Curating a new topic or collection

• I've formatted my changes as a new folder directory, named for the topic or collection as it appears in the URL on GitHub (e.g. https://github.com/topics/[NAME] or https://github.com/collections/[NAME])
• My folder contains a *.png image (if applicable) and index.md
• All required fields in my index.md conform to the Style Guide and API docs: https://github.com/github/explore/tree/main/docs

Please replace this line with an explanation of why you think this topic or collection should be curated.

Something that does not neatly fit into the binary options above

• My suggested edits are not about an existing topic or collection, or at least not a single one
• My suggested edits are not about curating a new topic or collection, or at least not a single one
• My suggested edits conform to the Style Guide and API docs: https://github.com/github/explore/tree/main/docs

Please replace this line with an explanation of your proposed changes.

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Please note: we will close your PR without comment if you do not check the boxes above and provide ALL requested information.

[github-actions]

Maintainer triage

Collection choosing-projects

Item	Stars	Last push	Owner type	Notes
rust-lang/rust	115,949	2026-08-23	Organization	–
Homebrew/brew	49,240	2026-08-23	Organization	–
https://www.youtube.com/embed/dSl_qnWO104	–	–	–	invalid format
public-apis/public-apis	468,773	2026-08-19	Organization	–
SerenityOS/serenity	33,770	2026-08-22	Organization	–
komodorio/helm-dashboard	5,745	2026-08-10	Organization	–
cloudquery/cloudquery	6,490	2026-08-22	Organization	–
Ileriayo/markdown-badges	16,978	2026-08-11	User	–
mem0ai/mem0	63,852	2026-08-23	Organization	–
Codecademy/docs	1,137	2026-02-27	Organization	archived
OpenSource-Communities/guestbook	508	2026-08-14	Organization	–
firstcontributions/first-contributions	55,634	2026-08-23	Organization	–