Add Usage chapter, fix test notifications example (#118)

docs/usage/basic-example.md

@@ -0,0 +1,68 @@
+# Basic example
+
+In this section we quickly go over a basic docker-compose file to run Diun using the docker provider.
+
+## Setup
+
+Create a `docker-compose.yml` file that uses the official Diun image:
+
+```yaml
+version: "3.5"
+
+services:
+  diun:
+    image: crazymax/diun:latest
+    volumes:
+      - "./data:/data"
+      - "/var/run/docker.sock:/var/run/docker.sock"
+    environment:
+      - "TZ=Europe/Paris"
+      - "LOG_LEVEL=info"
+      - "LOG_JSON=false"
+      - "DIUN_WATCH_WORKERS=20"
+      - "DIUN_WATCH_SCHEDULE=*/30 * * * *"
+      - "DIUN_PROVIDERS_DOCKER=true"
+      - "DIUN_PROVIDERS_DOCKER_WATCHBYDEFAULT=true"
+    restart: always
+```
+
+Here we use a minimal configuration to analyze **all running containers** (watch by default enabled) of your **local Docker** instance **every 30 minutes**.
+
+That's it. Now you can launch Diun with the following command:
+
+```shell
+$ docker-compose up -d
+```
+
+If you prefer to rely on the configuration file instead of environment variables:
+
+```yaml
+version: "3.5"
+
+services:
+  diun:
+    image: crazymax/diun:latest
+    volumes:
+      - "./data:/data"
+      - "./diun.yml:/diun.yml:ro"
+      - "/var/run/docker.sock:/var/run/docker.sock"
+    environment:
+      - "CONFIG=/diun.yml"
+      - "TZ=Europe/Paris"
+      - "LOG_LEVEL=info"
+      - "LOG_JSON=false"
+    restart: always
+```
+
+```yaml
+# ./diun.yml
+
+watch:
+  workers: 20
+  schedule: "*/30 * * * *"
+  firstCheckNotif: false
+
+providers:
+  docker:
+    watchByDefault: true
+```