Bootstrapping - dmd backend has been in D for a while

[Laeeth]

https://github.com/dlang/dmd/blob/master/src/dmd/backend/README.md

[timotheecour]

PRs welcome to update the info in this repo! as you can see here https://github.com/timotheecour/D_vs_nim/pulls?q=is%3Apr+is%3Aclosed I usually merge them pretty fast