Add Go report card

Author: kivattt

README.md

@@ -1,5 +1,7 @@
 Low on disk space? Use this tool to find the biggest files and folders on your Linux machine
 
+[![Go Report Card](https://goreportcard.com/badge/github.com/kivattt/fssize)](https://goreportcard.com/report/github.com/kivattt/fssize)
+
 <img src="screenshot.png" alt="fssize version v0.0.1 with the Folder tab selected">
 
 [The command-line parser stops parsing after the first non-option](https://stackoverflow.com/a/25113485).\