Fix contributing test instructions
#### Add the wasm target
```bash
-rustup add target wasm32-unknown-unknown
+rustup target add wasm32-unknown-unknown
```
#### Install [cargo-web]
@@ -41,3 +41,8 @@ although more driver support may be added! You can download these at:
```bash
./ci/run_tests.sh
```
+or
+
+```bash
+cargo test --target wasm32-unknown-unknown --features wasm_test
+```
