kvm,compute-offering: prevent CPU limiting completely

Related apache/cloudstack#12637

Signed-off-by: Abhishek Kumar <abhishek.mrt22@gmail.com>

Author: shwstppr

source/adminguide/service_offerings.rst

@@ -249,6 +249,9 @@ To create a new compute offering:
    -  **CPU cap**: Whether to limit the level of CPU usage even if spare
       capacity is available.
 
+      .. note::
+         On KVM hypervisor, to allow CloudStack to relinquish CPU usage control entirely, set this option to false and set CPU speed to zero. Note that Instances with zero CPU speed offerings should not be co-hosted with Instances using non-zero CPU speed offerings, as the CPU speed value is used as a relative weight (share) in the ``cputune`` section of the domain XML, and mixing zero and non-zero values would skew the weighting.
+
    -  **Volatile**: If checked, Instances created from this service offering
       will have their root disks reset upon reboot. This is useful for
       secure environments that need a fresh start on every boot and for