add goreportcard (#530)

README.md

@@ -12,6 +12,7 @@ It was inspired by _termbox_, but includes many additional improvements.
 [![Docs](https://img.shields.io/badge/godoc-reference-blue.svg?label=&logo=go)](https://pkg.go.dev/github.com/gdamore/tcell/v2)
 [![Discord](https://img.shields.io/discord/639503822733180969?label=&logo=discord)](https://discord.gg/urTTxDN)
 [![Coverage](https://img.shields.io/codecov/c/github/gdamore/tcell?logoColor=grey&logo=codecov&label=)](https://codecov.io/gh/gdamore/tcell)
+[![Go Report Card](https://goreportcard.com/badge/github.com/gdamore/tcell)](https://goreportcard.com/report/github.com/gdamore/tcell)
 
 Please see [here](UKRAINE.md) for an important message for the people of Russia.