documentation: remove old client version from the support matrix

[oz123]

Currently, the README contains a huge list of version of this clients with support for k8s clusters.
I find it odd that no one bothers to clean up... If there is no objection I would like to remove the versions from 1.5 to 1.10.
I seriously hope no one is still using k8s in these versions.
A nice side effect of this would be that the table will be completely visible in a 13" screen (not everyone has large HD screens).
Also I would like to clean the table containing support stati for the client. Again, I intend to remove versions 1.0 to 6.0.

@roycaihw @yliaog @micw523 what do you think?

[roycaihw]

removing versions <= Kubernetes 1.10 sounds good to me. Officially we support 3 stable major releases in this client, corresponding to 3 minor releases in Kubernetes

[micw523]

I’m not sure if some people are still using 1.10 on GKE (which was a thing when we were changing the CI from localkube to minikube last November). Removing 1.9 or lower sgtm.