add failure and success hooks

docs/markdown/location/hooks.md

@@ -2,7 +2,14 @@
 
 If you want to perform some commands before and/or after a backup, you can use hooks.
 
-They consist of a list of `before`/`after` commands that will be executed in the same directory as the target `from`.
+They consist of a list of commands that will be executed in the same directory as the target `from`.
+
+The following hooks groups are supported, none are required:
+
+- `before`
+- `after`
+- `failure`
+- `success`
 
 ```yml | .autorestic.yml
 locations:
@@ -11,10 +18,25 @@ locations:
     to: my-backend
     hooks:
       before:
-        - echo "Hello"
-        - echo "Human"
+        - echo "One"
+        - echo "Two"
+        - echo "Three"
       after:
-        - echo "kthxbye"
+        - echo "Byte"
+      failure:
+        - echo "Something went wrong"
+      success:
+        - echo "Well done!"
 ```
 
+## Flowchart
+
+1. `before` hook
+2. Run backup
+3. `after` hook
+4. - `success` hook if no errors were found
+   - `failure` hook if at least error was encountered
+
+If the `before` hook encounters errors the backup and `after` hooks will be skipped and only the `failed` hooks will run.
+
 > :ToCPrevNext