docs: Add a bare minimum doc for CentOS CI testing setup

Signed-off-by: Anoop C S <[email protected]>

Author: anoopcs9

docs/centosci-integration-tests.md

@@ -0,0 +1,20 @@
+### Run multinode kubernetes cluster tests with experimental CTDB support
+
+For every pull request on samba-operator repository, an integration test run
+is triggered on a [Jenkins](https://jenkins-samba.apps.ocp.cloud.ci.centos.org/view/SINK/)
+based pipeline from CentOS CI infrastructure which is supposed to show up in
+the list of GitHub checks along the following format:
+
+*centos-ci/sink-clustered/mini-k8s-latest*
+
+- Use the following text as GitHub comment to trigger a test run manually:
+
+  `/test centos-ci/sink-clustered/mini-k8s-latest`
+
+- Or if you want to re-run:
+
+  `/retest centos-ci/sink-clustered/mini-k8s-latest`
+
+- With more tests added to the matrix one could trigger everything at once with:
+
+  `/test all` or `/retest all`