CPU Ready (%RDY) is the percentage of time that a VM is ready to execute but has not been schedule for CPU time because it's waiting for a CPU to become available. This most often comes up when CPUs are oversubscribed. For example, a system has 16 physical CPUs but the sum of the number of vCPUs across all the VMs on that system is much greater than 16.
The general rule of thumb for a VM with 8 or less vCPUs is for %RDY to be between 8-10 ; otherwise, CPU contention is a factor. Next, since it's the summation of the all the vCPUs on that VM so %RDY may be higher with 32, 64, or 128 vCPUs. So a %RDY of 20 may be acceptable in those cases.
To remediate, make sure your VMs are right sized and that your host or cluster is not highly over-committed. Also, load balance your VMs across your hosts and clusters.