Fix link to Blackholio demo in Unreal tutorial and update project structure in README

[homersimpsons]

Description of Changes

Updated the link to target SpacetimeDB repository instead of archived blackholio repository.

Update the repository structure in the README.md to match the current one (also sort it alphabetically).

API and ABI breaking changes

NA

Expected complexity level and risk

1

Testing

Visit https://spacetimedb.com/docs/unreal/. this link is already used a bit below for the text "Blackhol.io"

[CLAassistant]

All committers have signed the CLA.

[homersimpsons]

I signed the CLA because my contribution is small. But note that I would prefer if there were no CLA https://drewdevault.com/2023/07/04/Dont-sign-a-CLA-2.html

Thank you for your work on this and on BitCraft too.

[bfops]

LGTM, thank you!

[bfops]

/update-llm-benchmarks

[clockwork-labs-bot]

LLM Benchmark Results (ci-quickfix)

Language	Mode	Category	Tests Passed	Pass %	Task Pass %
Rust	rustdoc_json	basics	19/27	70.4%	66.7%
Rust	rustdoc_json	schema	19/34	55.9%	53.3%
Rust	rustdoc_json	total	38/61	62.3%	60.6%
C#	docs	basics	27/27	100.0%	100.0%
C#	docs	schema	30/34	88.2%	86.7%
C#	docs	total	57/61	93.4%	93.9%

_{Generated at: 2026-01-12T18:08:56.998Z}

[bfops]

/update-llm-benchmarks