add minimal developer help in ReadME

README.md

@@ -4,3 +4,19 @@ The official ARC (annotated research context) website!
 
 [arc-rdm.org](https://www.arc-rdm.org)
 
+## Development
+
+### Requirements
+
+- [Node](https://nodejs.org/en) needs to be installed on your machine.
+
+### Local Build
+
+You can build the website locally, to verify the changes you make.
+
+In the command line, run:
+
+1. `npm install` to install the dependencies
+2. `npm run dev` to build the site in watch-mode
+
+Then, in the browser, navigate to the localhost address stated in the CI, e.g. `http://localhost:4321/`.