Add instructions for getting npm packages to build instructions.

worldwideportal-static/content/docs/setup-guide.md

@@ -181,6 +181,12 @@ The quickest option there is to run `curl https://sh.rustup.rs -sSf | sh`.
 
 `cargo install --locked trunk`
 
+### Install nodejs / npm
+
+Follow the instructions [here](https://nodejs.org/en/download/package-manager/) or get it from your package manager.
+
+It is only used to get packages from npm, so you don't need the latest and greatest.
+
 ### Build worldwideportal-server
 
 ```
@@ -193,6 +199,7 @@ popd
 
 ```
 pushd worldwideportal
+npm install
 trunk build --release
 popd
 ```