Update OpenShift pipelines-install instruction…

The current documentation doesn't work with OpenShift because of the
`securityContext.runAsUser` that comes in the way of the default
behavior of OpenShift. This fixes that.

Signed-off-by: Vincent Demeester <vdemeest@redhat.com>

content/en/vendor/redhat/pipelines-install.md

@@ -19,10 +19,14 @@ Constraints][security-con] for more information.
    ```
 1. Install Tekton Pipelines:
 
+    Because OpenShift uses random user id (and user id range per namespace) for pods, we need to remove the `securityContext.runAsUser` and `securityContext.runAsGroup` from any container from the release.yaml.
+    You will need to have [`yq`](https://mikefarah.gitbook.io/yq/) installed for this to work. Another way would be to download the yaml, search and replace (here replace with nothing) in your favourite editor.
+
    ```bash
-   oc apply --filename https://storage.googleapis.com/tekton-releases/pipeline/latest/release.notags.yaml
+   curl https://storage.googleapis.com/tekton-releases/pipeline/latest/release.notags.yaml | yq 'del(.spec.template.spec.containers[].securityContext.runAsUser, .spec.template.spec.containers[].securityContext.runAsGroup)' | oc apply -f -
    ```
 
+
    See the [OpenShift CLI documentation][openshift-cli] for more information on
    the `oc` command.