docs: edit contributing docs for rebuilding
Made it more explicit that you need to run yarn build alongside
docker-compose to rebuild concourse fully.
@@ -99,11 +99,19 @@ $ docker-compose up --build -d
This can be run while the original `docker-compose up` command is still running.
+If there are any changes to the web UI, you will also need to re-build:
+
+```sh
+$ yarn build
+```
+
+This can be run before or after the `docker-compose up` - the compiled assets
+will automatically propagate to the running containers.
+
### Working on the web UI
-We already showed how to run `yarn build` during the initial setup, but if
-you're actually working on the web UI you'll probably want to use `watch`
-instead:
+If you're actually working on the web UI you'll probably want to use `watch`
+instead of `build`:
```sh
$ yarn watch
