FIX added notes on multiple argo cd instances in the same cluster

[juanmatias]

What?

• Adde notes on how to deploy multiple cluster wide ArgoCD instances in the same cluster.

Why?

• If the step stated in the note is not done then the different instances will conflict.

References

• Two ArgoCD instances in different namespaces mixing Application definitions argoproj/argo-cd#18965

Important

Please include a screenshot of the pages that you modified to help reviewers. If you are using Chrome, you can follow the instructions below to easily take a full screenshot of the entire page:

1. Right click the page and open the inspector.
2. In the top left of Chrome Inspector you'll see a little phone icon whose tooltip shows "Toggle device emulation".
3. Hit that and a new black bar will appear on the top of the webpage.
4. In the black bar you can pick the dimensions of the screen you want to stimulate -- Since the documentation uses a responsive layout, you'll probably want to set a wide enough value on the width field, e.g. 1024x768, then the height is not as important.
5. In top right of black bar is three dots, in that menu you can do a full page screenshot.