New Topic: Endless Sky Plugins

[TheGiraffe3]

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 either the topic I am modifying/adding or the collection entry I am modifying/adding.

Which change are you proposing?

• Curating a new topic or collection

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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 (https://github.com/topics/endless-sky-plugins)
• 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

This topic should be curated because: See #4450.

[tomthorogood]

Thanks for this contribution. Now I'll have to download Endless Sky again 😢 👍