adds scaladoc badge to readme

Author: wookietreiber

README.md

@@ -2,6 +2,7 @@ Scala CLI Tools
 ===============
 
 [![Codacy Badge](https://api.codacy.com/project/badge/Grade/67d9aaafa59a414e9b808ef45abb3fb0)](https://www.codacy.com/app/wookietreiber/scala-cli-tools?utm_source=github.com&utm_medium=referral&utm_content=wookietreiber/scala-cli-tools&utm_campaign=Badge_Grade)
+[![Scaladoc](https://javadoc-badge.appspot.com/com.github.wookietreiber/scala-cli-tools_2.12.svg?label=scaladoc)](https://javadoc-badge.appspot.com/com.github.wookietreiber/scala-cli-tools_2.12)
 
 A collection of Scala command-line interface tools.