change problem-spring-web readme

[duliu1990]

Description

Spring Boot Web properties have some differences from version >=2.4, if version >=2.4 use below configuration:

spring:
  web:
    resources:
      add-mappings: false
  mvc:
    throw-exception-if-no-handler-found: true

Motivation and Context

Spring Boot 2.3.x version:
https://docs.spring.io/spring-boot/docs/2.3.x/reference/html/appendix-application-properties.html#common-application-properties

Spring Boot current version:

https://docs.spring.io/spring-boot/docs/current/reference/html/application-properties.html

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[cberg-zalando]

Will be handled via #915.