Curate: playdate topics

[boozook]

Please confirm this pull request meets the following requirements:

• [x] I followed the contributing guidelines: https://github.com/github/explore/blob/main/CONTRIBUTING.md.
• [x] 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?

• [ ] Suggesting edits to an existing topic or collection
• [x] 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

• [x] 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])
• [x] My folder contains a *.png image (if applicable) and index.md
• [x] All required fields in my index.md conform to the Style Guide and API docs: https://github.com/github/explore/tree/main/docs

I'm adding two new dependent topics:

• playdate (device, generic topic)
• playdate-sdk (SDK-related things, development)

First one playdate is more generic and I have seen many repositories with libs, frameworks, engines and games made for playdate, marked with this topic. Also projects like https://github.com/cranksters/playdate-reverse-engineering .

The second is playdate-sdk that concrete about the SDK, bindings/externs and development for platform in general. There are many projects with bindings for various languages such as swift, rust, nim, that marked with playdate-sdk topic. Also there are could be tools such as docs/code-generators and other tooling that uses SDK.

❗️ I'm adding two new topics because one depends on the other and they are both integral and necessary to each other.