Add a link to optim blog post (#5922)

Author: wing328

README.md

@@ -746,6 +746,7 @@ Here are some companies/projects (alphabetical order) using OpenAPI Generator in
 - 2020-03-02 - [OpenAPI Generator + TypeScript で始める自動生成の型に守られた豊かなクライアント生活](https://gift-tech.co.jp/articles/openapi-generator-typescript) by [五百蔵 直樹](https://gift-tech.co.jp/members/naokiioroi) at [GiFT株式会社](https://gift-tech.co.jp/)
 - 2020-03-10 - [OpenAPI Generator Meetup #1](https://speakerdeck.com/akihito_nakano/openapi-generator-meetup-number-1) by [中野暁人](https://github.com/ackintosh) at [OpenAPI Generator Meetup #1](https://openapi-generator-meetup.connpass.com/event/168187/)
 - 2020-03-15 - [Load Testing Your API with Swagger/OpenAPI and k6](https://k6.io/blog/load-testing-your-api-with-swagger-openapi-and-k6)
+- 2020-04-13 - [俺的【OAS】との向き合い方 (爆速でOpenAPIと友達になろう)](https://tech-blog.optim.co.jp/entry/2020/04/13/100000) in [OPTim Blog](https://tech-blog.optim.co.jp/)
 
 ## [6 - About Us](#table-of-contents)