docs: ask to give a star in README (#96)

Author: agneum

README.md

@@ -9,6 +9,19 @@ Provide developers access to experiment on automatically provisioned
 production-size DB testing replica. Joe will provide recommendations
 for query optimization and the ability to rollback.
 
+## Status
+
+The project is in its early stage. However, it is already being extensively used
+in some teams in their daily work. Since production is not involved, it is
+quite easy to try and start using it.
+
+Please support the project giving a GitLab star (it's on [the main page](https://gitlab.com/postgres-ai/joe),
+at the upper right corner):
+
+![Add a star](./assets/star.gif)
+
+To discuss Joe, [join our community Slack](https://database-lab-team-slack-invite.herokuapp.com/).
+
 ## Install Software
 
 ### 1. Database Lab