feat: add simple example

source/migration/index.ts

@@ -6,8 +6,41 @@
 
 ### Usage
 
-TODO: add simple example
+For instance, we have a simple set of rules:
 
+```yaml
+age:
+    question: "Quel est votre âge ?"
+````
+
+and the following situation:
+```json
+{
+    age: 25
+}
+```
+
+If I change my model because I want to fix the accent to:
+
+```yaml
+âge:
+    question: "Quel est votre âge ?"
+```
+
+I don't want to lose the previous answer, so I can use `migrateSituation` with the following migration instructions:
+
+```yaml
+keysToMigrate:
+    age: âge
+```
+
+Then, calling `migrateSituation` with the situation and the migration instructions will return:
+
+```json
+{
+    âge: 25
+}
+```
 */
 
 export * from './migrateSituation'