README: show of OpenSSF Scorecard badge

With the recent enabling of Scorecard updates, the badge accurately reflects
the current status. Let's show it...

README.md

@@ -1,6 +1,7 @@
 # A minimal logging API for Go
 
 [![Go Reference](https://pkg.go.dev/badge/github.com/go-logr/logr.svg)](https://pkg.go.dev/github.com/go-logr/logr)
+[![OpenSSF Scorecard](https://api.securityscorecards.dev/projects/github.com/go-logr/logr/badge)](https://securityscorecards.dev/viewer/?platform=github.com&org=go-logr&repo=logr)
 
 logr offers an(other) opinion on how Go programs and libraries can do logging
 without becoming coupled to a particular logging implementation.  This is not