Add env vars config example

docs/config/index.md

@@ -5,7 +5,7 @@
 There are two different ways to define configuration in Diun:
 
 * In a [configuration file](#configuration-file)
-* As environment variables
+* As [environment variables](#environment-variables)
 
 These ways are evaluated in the order listed above.
 
@@ -17,6 +17,7 @@ For example, the `DIUN_PROVIDERS_DOCKER` environment variable is enough by itsel
 
 You can define a configuration file through the option `--config` with the following content:
 
+??? example "diun.yml"
     ```yaml
     db:
       path: diun.db
@@ -96,6 +97,85 @@ providers:
         directory: ./imagesdir
     ```
 
+## Environment variables
+
+All configuration from file can be transposed into environment variables. As an example, the following configuration:
+
+??? example "diun.yml"
+    ```yaml
+    db:
+      path: diun.db
+    
+    watch:
+      workers: 10
+      schedule: "0 * * * *"
+      firstCheckNotif: false
+    
+    notif:
+      gotify:
+        endpoint: http://gotify.foo.com
+        token: Token123456
+        priority: 1
+        timeout: 10s
+      telegram:
+        token: aabbccdd:11223344
+        chatIDs:
+          - 123456789
+          - 987654321
+      webhook:
+        endpoint: http://webhook.foo.com/sd54qad89azd5a
+        method: GET
+        headers:
+          content-type: application/json
+          authorization: Token123456
+        timeout: 10s
+    
+    regopts:
+      someregistryoptions:
+        username: foo
+        password: bar
+        timeout: 20s
+    
+    providers:
+      kubernetes:
+        tlsInsecure: false
+        namespaces:
+          - default
+          - production
+    ```
+
+Can be transposed to:
+
+??? example "environment variables"
+    ```
+    DIUN_DB_PATH=diun.db
+    
+    DIUN_WATCH_WORKERS=10
+    DIUN_WATCH_SCHEDULE=0 * * * *
+    DIUN_WATCH_FIRSTCHECKNOTIF=false
+    
+    DIUN_NOTIF_GOTIFY_ENDPOINT=http://gotify.foo.com
+    DIUN_NOTIF_GOTIFY_TOKEN=Token123456
+    DIUN_NOTIF_GOTIFY_PRIORITY=1
+    DIUN_NOTIF_GOTIFY_TIMEOUT=10s
+    
+    DIUN_NOTIF_TELEGRAM_TOKEN=aabbccdd:11223344
+    DIUN_NOTIF_TELEGRAM_CHATIDS=123456789,987654321
+    
+    DIUN_NOTIF_WEBHOOK_ENDPOINT=http://webhook.foo.com/sd54qad89azd5a
+    DIUN_NOTIF_WEBHOOK_METHOD=GET
+    DIUN_NOTIF_WEBHOOK_HEADERS_CONTENT-TYPE=application/json
+    DIUN_NOTIF_WEBHOOK_HEADERS_AUTHORIZATION=Token123456
+    DIUN_NOTIF_WEBHOOK_TIMEOUT=10s
+    
+    DIUN_REGOPTS_SOMEREGISTRYOPTIONS_USERNAME=foo
+    DIUN_REGOPTS_SOMEREGISTRYOPTIONS_PASSWORD=bar
+    DIUN_REGOPTS_SOMEREGISTRYOPTIONS_TIMEOUT=20s
+    
+    PROVIDERS_KUBERNETES_TLSINSECURE=false
+    PROVIDERS_KUBERNETES_NAMESPACES=default,production
+    ```
+
 ## Reference
 
 * [db](db.md)