README: add badges

Author: dnaeon

README.md

@@ -1,5 +1,10 @@
 # go-binarytree
 
+[![Build Status](https://github.com/dnaeon/go-binarytree/actions/workflows/test.yaml/badge.svg)](https://github.com/dnaeon/go-binarytree/actions/workflows/test.yaml/badge.svg)
+[![Go Reference](https://pkg.go.dev/badge/gopkg.in/dnaeon/go-binarytree.v1.svg)](https://pkg.go.dev/gopkg.in/dnaeon/go-binarytree.v1)
+[![Go Report Card](https://goreportcard.com/badge/gopkg.in/dnaeon/go-binarytree.v1)](https://goreportcard.com/report/gopkg.in/dnaeon/go-binarytree.v1)
+[![codecov](https://codecov.io/gh/dnaeon/go-binarytree/branch/v1/graph/badge.svg)](https://codecov.io/gh/dnaeon/go-binarytree)
+
 A simple implementation of [Binary Trees](https://en.wikipedia.org/wiki/Binary_tree) in Go.
 
 ## Installation