Update README.md to include nvm use (#692)

Co-authored-by: Darren Temple <[email protected]>

README.md

@@ -24,6 +24,7 @@ You can check that the test suite works in your local environment by running it
 ``` bash
 git clone [email protected]:openactive/openactive-test-suite.git
 cd openactive-test-suite
+nvm use
 npm install
 npm start -- core
 ```