add maven doc

Author: alexcheng1982

README.md

@@ -6,4 +6,14 @@ Java Client for [FoodData Central API](https://fdc.nal.usda.gov/api-guide)
 
 Built with [OpenAPI Generator](https://openapi-generator.tech/) from [OpenAPI spec](https://api.nal.usda.gov/fdc/v1/yaml-spec?api_key=DEMO_KEY)
 
-> The OpenAPI spec is updated to fix mismatches with actual implementation.
+> The OpenAPI spec is updated to fix mismatches with actual implementation.
+
+Use this client in Maven.
+
+```xml
+<dependency>
+  <groupId>com.javaaidev</groupId>
+  <artifactId>usda-food-data-central-api-client</artifactId>
+  <version>1.3.0</version>
+</dependency>
+```