add zero-rails_openapi to implementations

Author: hikari-desu

IMPLEMENTATIONS.md

@@ -45,3 +45,4 @@ These tools are not necessarily endorsed by the OAI.
 | baucis-openapi3 | [Github/metadevpro/baucis-openapi3](https://github.com/metadevpro/baucis-openapi3) | Node.js | [Baucis.js](https://github.com/wprl/baucis) plugin for generating OpenAPI 3.0 compliant API contracts. |
 | Google Gnostic | [GitHub/googleapis/gnostic](https://github.com/googleapis/gnostic) | Go | Compile OpenAPI descriptions into equivalent Protocol Buffer representations. |
 | serverless-openapi-documentation | [GitHub/temando/serverless-openapi-documentation](https://github.com/temando/serverless-openapi-documentation) | Typescript | Serverless 1.0 plugin to generate OpenAPI V3 documentation from serverless configuration |
+| zero-rails_openapi | [GitHub/zhandao/zero-rails_openapi](https://github.com/zhandao/zero-rails_openapi) | Ruby | Provide concise DSL for generating the OpenAPI Specification 3 documentation file for Rails application |