Add trigger phrases and status badge for e2e tests

This adds the trigger phrases for the e2e tests to the README.md and
also the build badge for the periodic job.

Signed-off-by: Lennart Jern <lennart.jern@est.tech>

README.md

@@ -4,6 +4,7 @@
 [![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_daily_main_integration_test_ubuntu&subject=Ubuntu%20daily%20main)](https://jenkins.nordix.org/view/Metal3/job/metal3_daily_main_integration_test_ubuntu/)
 [![CentOS daily main build status](https://jenkins.nordix.org/buildStatus/icon?job=metal3_daily_main_integration_test_centos&subject=CentOS%20daily%20main)](https://jenkins.nordix.org/view/Metal3/job/metal3_daily_main_integration_test_centos/)
+[![BMO e2e periodic main](https://jenkins.nordix.org/view/Metal3%20Periodic/job/metal3-bmo-e2e-test-periodic/badge/icon)](https://jenkins.nordix.org/view/Metal3%20Periodic/job/metal3-bmo-e2e-test-periodic/)
 
 The Bare Metal Operator implements a Kubernetes API for managing bare metal
 hosts. It maintains an inventory of available hosts as instances of the
@@ -39,6 +40,11 @@ Eventually these tests will be replaced with BMO's own
 [e2e tests](test/e2e/README.md). BMO e2e tests are currently under active
 development. Here are the tests which run on different branches in BMO:
 
+**E2e tests:**
+
+* **/test metal3-bmo-e2e-test-pull** runs required BMO e2e tests on your PR. Works for main and release-0.5 branches.
+* **/test metal3-bmo-e2e-test-optional-pull** runs optional BMO e2e tests on your PR. These are under active development currently.
+
 **Main branch:**
 
 * **/test-centos-e2e-integration-main** runs CAPM3 e2e integration tests with