Update README.md

Author: alexcheng1982

README.md

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 # USDA FoodData Central API Client
 
-[![build](https://github.com/JavaAIDev/usda-fooddata-central-api-client/actions/workflows/build.yaml/badge.svg)](https://github.com/JavaAIDev/usda-fooddata-central-api-client/actions/workflows/build.yaml)
+[![build](https://github.com/JavaAIDev/usda-fooddata-central-api-client/actions/workflows/build.yaml/badge.svg)](https://github.com/JavaAIDev/usda-fooddata-central-api-client/actions/workflows/build.yaml)
+
+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.