Docs website with mkdocs (#100)

* Fix build workflow

* Docs website with mkdocs (#99)

* Fix docs workflow

* Move mkdocs Docker file

* Ignore docs in build workflow

* Update workflows

* Update links

* Move upgrade notes to documentation

Co-authored-by: CrazyMax <crazy-max@users.noreply.github.com>

docs/migration/v0-to-v1.md

@@ -0,0 +1,43 @@
+# Diun v0 to v1
+
+Some fields in configuration file has been changed:
+
+* `registries` renamed `regopts`
+* `items` renamed `image`
+* `items[].image` renamed `image[].name`
+* `items[].registry_id` renamed `image[].regopts_id`
+* `watch.os` and `watch.arch` moved to `image[].os` and `image[].arch`
+
+!!! example "v0"
+    ```yaml
+    watch:
+      os: linux
+      arch: amd64
+    
+    registries:
+      someregistryoptions:
+        username: foo
+        password: bar
+        timeout: 20
+    
+    items:
+      - image: docker.io/crazymax/nextcloud:latest
+        registry_id: someregistryoptions
+    ```
+
+!!! example "v1"
+    ```yaml
+    watch:
+      os: linux
+      arch: amd64
+    
+    registries:
+      someregistryoptions:
+        username: foo
+        password: bar
+        timeout: 20
+    
+    items:
+      - image: docker.io/crazymax/nextcloud:latest
+        registry_id: someregistryoptions
+    ```

docs/migration/v1-to-v2.md

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+# Diun v1 to v2
+
+`image` field has been moved to `providers.static` in configuration file:
+
+!!! example "v1"
+    ```yaml
+    image:
+      - name: docker.io/crazymax/diun
+        watch_repo: true
+        max_tags: 10
+    ```
+
+!!! example "v2"
+    ```yaml
+    providers:
+      static:
+        - name: docker.io/crazymax/diun
+          watch_repo: true
+          max_tags: 10
+    ```

docs/migration/v2-to-v3.md

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+# Diun v2 to v3
+
+## File provider
+
+`static` provider has been renamed `file`. This now allows the static configuration to be declared in one or more files to avoid overloading the current configuration file and also dynamic updating.
+
+!!! example "v2"
+    ```yaml
+    providers:
+      static:
+        - name: docker.io/crazymax/diun
+          watch_repo: true
+          max_tags: 10
+    ```
+
+!!! example "v3"
+    ```yaml
+    providers:
+      file:
+        # Watch images from filename /path/to/config.yml
+        filename: /path/to/config.yml
+        # OR watch images from directory /path/to/config/folder
+        directory: /path/to/config/folder
+    ```
+    ```yaml
+    # /path/to/config.yml
+    - name: docker.io/crazymax/diun
+      watch_repo: true
+      max_tags: 10
+    ```
+
+## Allow only one Docker and Swarm provider
+
+Now you can declare only one Docker and/or Swarm provider. This is due to a limitation of the Docker engine.
+
+!!! example "v2"
+    ```yaml
+    providers:
+      docker:
+        mydocker:
+          watch_stopped: true
+      swarm:
+        myswarm:
+          watch_by_default: true
+    ```
+
+!!! example "v3"
+    ```yaml
+    providers:
+      docker:
+        watch_stopped: true
+      swarm:
+        watch_by_default: true
+    ```
+
+## Remove `enable` setting for notifiers
+
+The `enable` entry has been removed for notifiers. If you don't want a notifier to be enabled, you must now remove or comment its configuration.
+
+!!! example "v2"
+    ```yaml
+    notif:
+      amqp:
+        enable: false
+        host: localhost
+        port: 5672
+      gotify:
+        enable: true
+        endpoint: http://gotify.foo.com
+        token: Token123456
+        priority: 1
+        timeout: 10
+    ```
+
+!!! example "v3"
+    ```yaml
+    notif:
+      gotify:
+        endpoint: http://gotify.foo.com
+        token: Token123456
+        priority: 1
+        timeout: 10
+    ```