Add node version and firefox notes to local setup doc

docs/setup.md

@@ -16,6 +16,8 @@ Dependencies:
 
 We recommend using [RBenv](https://github.com/rbenv/rbenv) to manage Ruby versions.
 
+We recommend using [nvm](https://github.com/nvm-sh/nvm) to manage NodeJS versions.
+
 1. Install PostgreSQL
 
     macOS:
@@ -70,10 +72,12 @@ We recommend using [RBenv](https://github.com/rbenv/rbenv) to manage Ruby versio
 
 5. Install JavaScript dependencies
 
-    macOS:
+   Note that we currently use node v16, which is no longer the latest LTS version so you will need to specify the version number when installing
 
+    macOS (using nvm):
    ```bash
-    brew install node
+   nvm install 16
+   nvm use 16
    brew install yarn
    ```
 
@@ -168,6 +172,8 @@ We recommend using [RBenv](https://github.com/rbenv/rbenv) to manage Ruby versio
     bundle exec rspec
     ```
    
+    Note that these tests assume you have firefox installed.
+
 ## Using Docker
 
 1. Build the image: