Update ScalaRequestBinders.md by SunPj · Pull Request #13320 · playframework/playframework

Adding routesImport section which is essential to use custom routing binders. Without adding it a user wont' be able to use the binders he implements.

Fixes

Fixes documentation wasn't complete. I have added the missing part

Purpose

To make the documentation complete so users don't get confused with error like "No QueryString binder found for type ..."

Background Context

I faced the same issues when I forgot to import the custom binders but when I checked the docs I didn't find that mentioned so I decided to complete to docs