docs: add readme badges for test passing and coverage

README.md

@@ -1,8 +1,13 @@
 # SQLNull
+![go-version-badge](https://img.shields.io/github/go-mod/go-version/gkits/sqlnull)
+![test-pipeline-badge](https://github.com/gkits/sqlnull/actions/workflows/test.yml/badge.svg)
+![test-coverage-badge](https://raw.githubusercontent.com/gKits/sqlnull/badges/.badges/main/coverage.svg)
 
 A dead simple one stop solution to pass your database types directly to
 your JSON REST-API.
 
+---
+
 This package provides wrapper types for all Null* types of the 
 [`database/sql`](https://pkg.go.dev/database/sql) which implement the 
 `Marshaler` and `Unmarshaler` interface of the