Add OSINT GitHub Topic

[mtthlm]

Please confirm this pull request meets the following requirements:

• I followed the contributing guidelines: https://github.com/github/explore/blob/main/CONTRIBUTING.md.
• I am not the sole author or employee of a company who created the topic or collection I'm changing.

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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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

OSINT is an ever increasing field of interest, not just for government purposes or personal purposes, but also commercial purposes. As an engineer always on the lookout for new tools, projects, technologies - I thought the topic deserved an official place of it's own.

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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.

[ahpook]

LGTM, thanks for the contribution! 👍