Document development options.

README.md

@@ -15,6 +15,17 @@ yarn run webpack --mode production
 
 This will download all dependencies and compile javascript as needed.
 
+For development, you can run the following:
+
+```bash
+composer update
+yarn
+yarn watch &
+yarn serve
+```
+
+when you do, a PHP built-in web server will launch.
+
 ## Installation
 
 After building, you can install the project on your web server by copying