Completed the Credits section

docs/credits.md

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 # Credits
+
+I’m not working alone on this project. First, many people create PR for this
+projects. Then, there is the whole #pinetime community : a lot of people all
+around the world who are hacking, searching, experimenting and programming the
+Pinetime. We exchange our ideas, experiments and code in the chat rooms and
+forums.
+
+Here are some people I would like to highlight:
+
+ - [Atc1441](https://github.com/atc1441/) : He works on an Arduino based
+   firmware for the Pinetime and many other smartwatches based on similar
+   hardware. He was of great help when I was implementing support for the BMA421
+   motion sensor and I²C driver.
+ - [Koen](https://github.com/bosmoment) : He’s working on a firmware based on
+   RiotOS. He integrated similar libs as me : NimBLE, LittleVGL,… His help was
+   invaluable too!
+ - [Lup Yuen Lee](https://github.com/lupyuen) : He is everywhere: he works on a
+   Rust firmware, builds a MCUBoot based bootloader for the Pinetime, designs a
+   Flutter based companion app for smartphones and writes a lot of articles
+   about the Pinetime!
+
+*If you feel like you should appear on this list, just get in touch with me or submit a PR :)*
+