doc(README): indicate how to upgrade schema

README.md

@@ -2,6 +2,12 @@
 
 A simple command line client written in Rust that use Duniter GVA API.
 
-This example project is more there to show the way for those who would like to develop Rust projects using GVA :)
+## Contribute
+
+Contributions are welcome :)
 
 If you have any questions about the code don't hesitate to ask @elois on the duniter forum: [https://forum.duniter.org](https://forum.duniter.org)
+
+The GraphQL schema is automatically generated from the GVA source code, to update the schema, use the following command:
+
+cargo update -p duniter-gva-gql