Added pkg.go.dev badge to README

Added the reference pkg.go.dev badge to README.md

Author: kairoaraujo

README.md

@@ -2,6 +2,7 @@
 
 [![Go Report Card](https://goreportcard.com/badge/github.com/kairoaraujo/goca)](https://goreportcard.com/report/github.com/kairoaraujo/goca)
 [![Build Status](https://github.com/kairoaraujo/goca/workflows/tests/badge.svg)](https://github.com/kairoaraujo/goca/actions)
+[![Go Reference](https://pkg.go.dev/badge/github.com/kairoaraujo/goca.svg)](https://pkg.go.dev/github.com/kairoaraujo/goca)
 
 Package GocA provides a Certificate Authority (CA) framework managing.