Update website/README.md

Co-authored-by: Ólafur Páll Geirsson <[email protected]>

Author: jdorfman

website/README.md

@@ -12,6 +12,10 @@ $ yarn install
 
 ```bash
 $ cd website/
+# In one terminal window, requires a Java installation
+$ ./sbt "docs/mdoc -w"
+# In a separate terminal window
+$ cd website/
 $ yarn run start
 ```