Non consistent naming of PartitionSet/PartitionGroup

[stolsma]

Small nit...

The main README.md text and pictures are not consistent regarding PartitionSet/PartitionGroup naming. It makes it very difficult to understand the flow of actions... Could the pictures or the text be changed to reflect the correct naming?

Its the part below the 'How it works' line. Specifically the following text and corresponding diagram:

"The Atomix controller provides two custom Kubernetes controllers for managing partition groups and partitions. When a partition group is created via the Atomix controller API, the Atomix controller creates a PartitionSet resource, and the remainder of the deployment process is managed by custom Kubernetes controllers. The PartitionSet controller creates a set of Partition resources from the PartitionSet, and the Partition controller creates StatefulSet resources, Services, and other resources necessary to run the protocol specified by the PartitionSet configuration."

Thanks!!

Could have make a pull request but I don't have access to the original picture...