I see that you intend to contribute to the Nim repo, so you would have already done the cloning step in step 1 in the instructions at [https://github.com/nim-lang/Nim#compiling](https://github.com/nim-lang/Nim#compiling).
For unix systems, step 2 is `sh build_all.sh`. And then `koch docs` creates the whole Nim documentation website locally.
