Change docs target

[finestructure]

As discussed, this

• removes the extra package manifest in Documentation
• flattens the directory structure in Documentation
• adds the SwiftBundler documentation target to the main manifest
• updates update-docs.yml to the new directory structure

I don't think there's a way to test update-docs.yml prior to merging into main, is there?

[stackotter]

Thanks for the PR, looks good 👍 Sadly I don't think there's a way to test the workflow before merging, so we'll just have to cross our fingers 🤞 It looks like it should work

[finestructure]

Looks like it worked, nice!

[stackotter]

I'll be very excited to see documentation generation added to SPI, so good luck! I've always been jealous of rust's cargo for that