Switch from floryn90/hugo to hugomods/hugo image

The site build fails since floryn90/hugo v0.134.3:

```
Error: error building site: failed to acquire a build lock: open /src/.hugo_build.lock: permission denied
```

Cause: The Alpine image has switched from root user to hugo user:

floryn90/docker-hugo@b261630

Fix: Switch to hugomods/hugo image that still runs as root user.

The hugomods/hugo:std-exts image has git included making our Dockerfile obsolete.

README.md

@@ -69,20 +69,12 @@ than [Docker Desktop](https://www.docker.com/products/docker-desktop) on
 Windows and Mac, and [Docker Compose](https://docs.docker.com/compose/install/)
 on Linux.
 
-1. Build the docker image
-
-   ```bash
-   docker-compose build
-   ```
-
-1. Run the built image
+1. Spin up the service
 
    ```bash
    docker-compose up
    ```
 
-   > NOTE: You can run both commands at once with `docker-compose up --build`.
-
 1. Verify that the service is working.
 
    Open your web browser and type `http://localhost:1313` in your navigation bar,
@@ -94,7 +86,7 @@ on Linux.
 
 To stop Docker Compose, on your terminal window, press **Ctrl + C**.
 
-To remove the produced images run:
+To remove the produced container run:
 
 ```bash
 docker-compose rm

docker-compose.yaml

@@ -3,11 +3,10 @@ version: "3.8"
 services:
 
   site:
-    image: docsy/docsy-example
-    build:
-      context: .
-    command: server
-    ports:
-      - "1313:1313"
+    image: hugomods/hugo:std-exts
+    command: server -D
     volumes:
-      - .:/src
+      - ./:/src
+      - ~/hugo_cache:/tmp/hugo_cache
+    ports:
+      - 1313:1313