add openssf best practices badge to README

We have achieved passing badge on OpenSSF Best Practices. Adding badge
to key repositories to display this achievement. It is also checked
by the CLOmonitor and is required to move up to incubated project in
CNCF.

Signed-off-by: Tuomo Tanskanen <[email protected]>

README.md

@@ -1,6 +1,7 @@
 # Bare Metal Operator
 
 [![CLOMonitor](https://img.shields.io/endpoint?url=https://clomonitor.io/api/projects/cncf/metal3-io/badge)](https://clomonitor.io/projects/cncf/metal3-io)
+[![OpenSSF Best Practices](https://www.bestpractices.dev/projects/9160/badge)](https://www.bestpractices.dev/projects/9160)
 [![OpenSSF Scorecard](https://api.securityscorecards.dev/projects/github.com/metal3-io/baremetal-operator/badge)](https://securityscorecards.dev/viewer/?uri=github.com/metal3-io/baremetal-operator)
 [![Ubuntu daily main build status](https://jenkins.nordix.org/buildStatus/icon?job=metal3-periodic-ubuntu-e2e-integration-test-main&subject=Ubuntu%20daily%20main)](https://jenkins.nordix.org/view/Metal3/job/metal3-periodic-ubuntu-e2e-integration-test-main/)
 [![CentOS daily main build status](https://jenkins.nordix.org/buildStatus/icon?job=metal3-periodic-centos-e2e-integration-test-main&subject=CentOS%20daily%20main)](https://jenkins.nordix.org/view/Metal3/job/metal3-periodic-centos-e2e-integration-test-main/)