docs: document --target cross-compilation flag

- Add cross-compilation to README.md features and quick start
- Add cross-compilation section to docs/BuildAndTest.md

README.md

@@ -24,6 +24,9 @@ cd hello
 
 # Build and run
 bux run
+
+# Cross-compile for ARM Linux (requires clang)
+bux build --target aarch64-linux-gnu
 ```
 
 ---
@@ -201,6 +204,7 @@ func Main() -> int {
 | **CTFE** | `const func` — compile-time function execution |
 | **Trait Bounds** | `func Max<T: Comparable>(a: T, b: T) -> T` |
 | **Package Manager** | `bux add`, `bux install`, `bux.lock`, path + git deps |
+| **Cross-Compilation** | `--target <triple>` via clang (e.g. `aarch64-linux-gnu`) |
 | **Tooling** | `bux new`, `bux build`, `bux run`, `bux test`, `bux check` |
 
 ---

docs/BuildAndTest.md

@@ -107,6 +107,24 @@ Output = "Bin"
 
 Build output goes to `build/` by default.
 
+### Cross-Compilation
+
+Use `--target <triple>` to cross-compile for a different platform. Bux generates C code and uses `clang` with the `-target` flag for cross-compilation.
+
+```bash
+# Cross-compile for ARM Linux
+./buxc build --target aarch64-linux-gnu
+
+# Cross-compile for x86_64 Linux (explicit)
+./buxc build --target x86_64-linux-gnu
+
+# Cross-compile and run project build
+./buxc project --target x86_64-linux-gnu
+./buxc run --target aarch64-linux-gnu
+```
+
+> **Note:** `clang` must be installed for cross-compilation. Without `--target`, Bux uses the system `cc` compiler.
+
 ---
 
 ## Running Tests