Clarify native runtime builds

source/README.md

@@ -10,14 +10,18 @@ prebuilt runtime automatically.
 
 ## Build
 
-Install Go 1.26.1 or newer, then run:
+Install Go 1.26.1 or newer on the target platform, then run:
 
 ```bash
 go build -o vigil-runtime ./cmd/vigil-compact
 ```
 
+Build each operating system and architecture on a matching native runner. The
+ONNX Go binding is platform-specific and is not intended for
+`CGO_ENABLED=0` cross-compilation.
+
 The resulting binary dynamically loads ONNX Runtime when it starts. Pass the
-shared library, model, and metadata paths as shown by `vigil-runtime`:
+shared library, model, and metadata paths to the runtime:
 
 ```bash
 ./vigil-runtime \