Added javadoc badge.

Author: javadev

README.md

@@ -4,6 +4,7 @@
 [![MIT License](http://img.shields.io/badge/license-MIT-green.svg) ](https://github.com/javadev/leetcode-in-kotlin/blob/main/LICENSE)
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+[![javadoc](https://javadoc.io/badge2/com.github.javadev/leetcode-in-kotlin/javadoc.svg)](https://javadoc.io/doc/com.github.javadev/leetcode-in-kotlin)
 
 Kotlin Solution for LeetCode algorithm problems, continually updating.