docs: add Nikkei to user list (#4253)
docs: add Nikkei to user list (#4253)

Signed-off-by: TakahiroTsuruda <a8281febd014533ebc9f8e08c49174ac194e0cc3@gmail.com>
argoproj/argo-cd,argoproj/argo-cd,argoproj/argo-cd,argoproj/argo-cd,argoproj/argo-cd