Add how to to readme

Author: jerowork

README.md

@@ -1,2 +1,14 @@
 # Example application - GraphQL Attribute Schema
-Example application demonstrating [jerowork/graphql-attribute-schema](https://github.com/jerowork/graphql-attribute-schema).
+Example application demonstrating [jerowork/graphql-attribute-schema](https://github.com/jerowork/graphql-attribute-schema).
+
+## How to run
+Start the local webserver with Symfony:
+```bash
+symfony server:start
+```
+
+When started, the GraphQL endpoint is accessible at: http://127.0.0.1:8000/graphql (POST-requests only).
+
+It uses a SQLite database, nothing more needed, enjoy! 😎
+
+Note: It's recommended to use a GraphQL GUI like [GraphiQL](https://github.com/graphql/graphiql) or [Altair GraphQL Client](https://altairgraphql.dev/).