Update docs to explain restore hooks feature and add a migration guide

docs/markdown/migration/1.7_1.8.md

@@ -0,0 +1,45 @@
+# Migration from `1.7` to `1.8`
+
+## Config files
+
+- The config version have been changed
+- You can now configure restore hooks
+
+See detailed instructions below.
+
+## Config Version
+
+The version field of the config file has been changed from `2` to `3`.
+
+## Hooks
+
+Since `1.8` both backup and restore hooks are possible.
+For this reason, backup hooks have been moved one layer deeper, you have to move them in a `backup` object.
+
+Before:
+
+```yaml
+locations:
+  l1:
+    # ...
+    from: /foo/bar
+    hooks:
+      before:
+        - pwd
+```
+
+After:
+
+```yaml
+locations:
+  l1:
+    # ...
+    from: /foo/bar
+    hooks:
+      backup:
+        before:
+          - pwd
+      restore:
+        after:
+          - echo "My super restore hook"
+```

docs/markdown/migration/index.md

@@ -2,3 +2,4 @@
 
 - [From 0.x to 1.0](/migration/0.x_1.0)
 - [From 1.4 to 1.5](/migration/1.4_1.5)
+- [From 1.7 to 1.8](/migration/1.7_1.8)