Update README.md

Author: malczuuu

README.md

@@ -2,6 +2,7 @@
 
 [![JitPack](https://jitpack.io/v/malczuuu/problem4j-core.svg)](https://jitpack.io/#malczuuu/problem4j-core)
 [![Build Status](https://github.com/malczuuu/problem4j-jackson/actions/workflows/gradle.yml/badge.svg)](https://github.com/malczuuu/problem4j-jackson/actions/workflows/gradle.yml)
+[![Weekly Build Status](https://github.com/malczuuu/problem4j-jackson/actions/workflows/gradle-weekly.yml/badge.svg)](https://github.com/malczuuu/problem4j-jackson/actions/workflows/gradle-weekly.yml)
 
 > Part of [`problem4j`][problem4j] package of libraries.