SpringBoot Document additional configuration that is required for spring.mvc.throw-exception-if-no-handler-found=true to be effective

spring.mvc.throw-exception-if-no-handler-found=true requires additional configuration to be effective because default +spring.mvc.static-path-pattern=/**+ collides it. This PR explains correlation, which is confusing. The confusion was reported in https://github.com/spring-projects/spring-boot/issues/9263 and others

Comment From: wilkinsona

See https://gitter.im/spring-projects/spring-boot?at=62ba1378568c2c30d30790af for a little bit of background.

Comment From: wilkinsona

@michaldo Thanks for your patience and for making your first contribution to Spring Boot.