Update doc/manual/source/development/building.md

Co-authored-by: John Ericson <[email protected]>

Author: Mic92

doc/manual/source/development/building.md

@@ -213,6 +213,17 @@ nix build .#nix-everything-x86_64-unknown-freebsd
 nix build .#nix-everything-x86_64-w64-mingw32
 ```
 
+For historic reasons and backward-compatibility, some CPU and OS identifiers are translated as follows:
+
+| `config.guess`             | Nix                 |
+|----------------------------|---------------------|
+| `amd64`                    | `x86_64`            |
+| `i*86`                     | `i686`              |
+| `arm6`                     | `arm6l`             |
+| `arm7`                     | `arm7l`             |
+| `linux-gnu*`               | `linux`             |
+| `linux-musl*`              | `linux`             |
+
 ## Compilation environments
 
 Nix can be compiled using multiple environments: