Update openapi.md (#2105)

Co-authored-by: Adam Warski <adam@warski.org>

docs/openapi.md

@@ -1,13 +1,7 @@
 # OpenAPI
 
-sttp-client [request definitions](requests/basics.md) can be automatically generated from [openapi](https://swagger.io/specification/) `.yaml` specifications using:
-
-1. the [sttp-openapi-generator](https://github.com/ghostbuster91/sttp-openapi-generator)
-2. the `scala-sttp` code generator, included in the [openapi-generator](https://github.com/OpenAPITools/openapi-generator) project
-
-## Using sttp-openapi-generator
-
-See the project's [docs](https://github.com/ghostbuster91/sttp-openapi-generator).
+sttp-client [request definitions](requests/basics.md) can be automatically generated from [openapi](https://swagger.io/specification/) `.yaml` specifications using
+the `scala-sttp` code generator, included in the [openapi-generator](https://github.com/OpenAPITools/openapi-generator) project.
 
 ## Using the openapi-generator
 
@@ -30,6 +24,10 @@ openapi-generator-cli generate \
   -o samples/client/petstore/
 ```
 
+### Maven managed
+
+For maven project use plugin [openapi-generator-maven-plugin](https://github.com/OpenAPITools/openapi-generator/tree/master/modules/openapi-generator-maven-plugin)
+
 ### Sbt managed
 
 In this setup openapi-generator is plugged into sbt project through the [sbt-openapi-generator](https://github.com/OpenAPITools/sbt-openapi-generator/) plugin.