Apply patch from alanyih to correct name for worker in README.md

The image name should be worker instead of obs-worker in our script.
This patch updates the correct image name for worker in README.md.

Signed-off-by: Andrew Lee (李健秋) <andrew.lee@collabora.co.uk>

README.md

@@ -36,13 +36,13 @@
 1. Run the containers (local developer mode)
    ```
    $ docker-compose up
-   $ docker-compose scale obs-worker=2
+   $ docker-compose scale worker=2
    ```
 
 2. Run the containers (production mode with images from CI Container Registry)
    ```
    $ docker-compose -f docker-compose.yml -f docker-compose.prod.yml up
-   $ docker-compose scale obs-worker=2
+   $ docker-compose scale worker=2
    ```
 
 == Access Open Build Service UI ==