crux-mir README: Update translate_libs.sh usage

crux-mir/README.md

@@ -28,18 +28,17 @@ Use 8.10.7, 9.2.7, or 9.4.4.  From the `crux-mir` directory, run:
 
     $ cabal v2-install exe:crux-mir --overwrite-policy=always
 
-Then translate the Rust libraries in `lib/` (requires
-[`jq`](https://jqlang.github.io/jq/)):
+Then translate the Rust libraries in `lib/`:
 
     $ ./translate_libs.sh
 
-If you want to cross-compile for a different target, you can pass a [target
-triple](https://doc.rust-lang.org/nightly/rustc/platform-support.html) as an
-optional argument to `./translate_libs.sh`. This is experimental and we have
-only tested `wasm32-unknown-unknown` to work; you might get build errors for
-other targets.
+If you want to cross-compile for a different target, you can optionally set the
+environment variable `TARGET` to a [target
+triple](https://doc.rust-lang.org/nightly/rustc/platform-support.html) when
+running `./translate_libs.sh`. This is experimental and we have only tested
+`wasm32-unknown-unknown` to work; you might get build errors for other targets.
 
-    $ ./translate_libs.sh wasm32-unknown-unknown
+    $ TARGET=wasm32-unknown-unknown ./translate_libs.sh
 
 When upgrading from a previous version, first install the new `mir-json`
 version, then rerun the `cabal v2-install` and `./translate_libs.sh` commands.