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/notif/script.md

@@ -0,0 +1,40 @@
+# Script notifications
+
+You can call a script when a notification occured. Following environment variables will be passed:
+
+```
+DIUN_VERSION=3.0.0
+DIUN_ENTRY_STATUS=new
+DIUN_ENTRY_PROVIDER=file
+DIUN_ENTRY_IMAGE=docker.io/crazymax/diun:latest
+DIUN_ENTRY_HUBLINK=https://hub.docker.com/r/crazymax/diun
+DIUN_ENTRY_MIMETYPE=application/vnd.docker.distribution.manifest.list.v2+json
+DIUN_ENTRY_DIGEST=sha256:216e3ae7de4ca8b553eb11ef7abda00651e79e537e85c46108284e5e91673e01
+DIUN_ENTRY_CREATED=2020-03-26 12:23:56 +0000 UTC
+DIUN_ENTRY_PLATFORM=linux/amd64
+```
+
+## Configuration
+
+!!! example "File"
+    ```yaml
+    notif:
+      script:
+        cmd: "myprogram"
+        args:
+          - "--anarg"
+          - "another"
+    ```
+
+| Name                  | Default       | Description   |
+|-----------------------|---------------|---------------|
+| `cmd`[^1]             |               | Command or script to execute |
+| `args`                |               | List of args to pass to `cmd` |
+| `dir`                 |               | Specifies the working directory of the command |
+
+!!! abstract "Environment variables"
+    * `DIUN_NOTIF_SCRIPT_CMD`
+    * `DIUN_NOTIF_SCRIPT_ARGS`
+    * `DIUN_NOTIF_SCRIPT_DIR`
+
+[^1]: Value required