Added a image of new cluster form for README.
Added a image of new cluster form for README.

GoogleCloudPlatform/cloud-bigtable-examples,nlpraveennl/cloud-bigtable-examples,sduskis/cloud-bigtable-examples,GoogleCloudPlatform/cloud-bigtable-examples,sduskis/cloud-bigtable-examples,nlpraveennl/cloud-bigtable-examples,sduskis/cloud-bigtable-examples,sduskis/cloud-bigtable-examples,sduskis/cloud-bigtable-examples,nlpraveennl/cloud-bigtable-examples,GoogleCloudPlatform/cloud-bigtable-examples,GoogleCloudPlatform/cloud-bigtable-examples,sduskis/cloud-bigtable-examples,nlpraveennl/cloud-bigtable-examples,sduskis/cloud-bigtable-examples