Add Zig topic

[data-man]

Thank you for contributing! Please confirm this pull request meets the following requirements:

• I followed the contributing guidelines: https://github.com/github/explore/blob/master/CONTRIBUTING.md
• I have no affiliation with the project I am suggesting (as a maintainer, creator, contractor, or employee).

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/master/docs

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

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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.

[data-man]

cc @andrewrk

[deniseyu]

Thanks for the contribution, @data-man!

[data-man]

Thank you!