add r/place reference links and resources

Curated collection of official post-mortems, technical walkthroughs,
open-source implementations, and live instances for r/place research.

docs/references.md

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+# References
+
+## Official / Post-mortems
+
+- [How We Built r/place (Reddit)](https://redditinc.com/news/how-we-built-rplace)
+- [How We Built r/place 2022 - Backend Part 1](https://www.reddit.com/r/RedditEng/comments/vwv2fl/how_we_built_rplace_2022_backend_part_1_backend/)
+- [Reddit on Building & Scaling r/place (Fastly)](https://www.fastly.com/blog/reddit-on-building-scaling-rplace)
+- [Engineering Behind r/place](https://saikumarchintada.medium.com/engineering-behind-r-place-a7eb53bcf5f1)
+
+## Technical Walkthroughs
+
+- [Redis Place: Building r/place with 9 Redis Data Structures](https://dev.to/mehdi/redis-place-building-rplace-with-9-redis-data-structures-3lj8)
+- [Redis Pixel War](https://dev.to/alfredosalzillo/redis-pixel-war-3i7a)
+- [Reddit r/place - How It Works](https://tejash.dev/posts/reddit-rplace)
+- [Redis BITFIELD Command](https://redis.io/docs/latest/commands/bitfield/)
+
+## Open-Source Implementations
+
+- [reddit-plugin-place-opensource (Reddit Archive)](https://github.com/reddit-archive/reddit-plugin-place-opensource)
+- [rPlace by anthonytedja](https://github.com/anthonytedja/rPlace)
+- [redis-place by mehdiamrane](https://github.com/mehdiamrane/redis-place)
+- [redis-challenge by alfredosalzillo](https://github.com/alfredosalzillo/redis-challenge)
+- [place by dynastic](https://github.com/dynastic/place)
+
+## Live Instances
+
+- [rplace.live](https://rplace.live/)