vm: note on vmware disk controllers (#314)

Signed-off-by: Abhishek Kumar <abhishek.mrt22@gmail.com>
Co-authored-by: dahn <daan.hoogland@gmail.com>

Author: shwstppr

source/adminguide/virtual_machines.rst

@@ -165,6 +165,15 @@ To create a VM from a template:
    functions such as mounting additional volumes and ISO images,
    live migration, and graceful shutdown.
 
+   **VMware**
+
+   If the rootDiskController and dataDiskController are not specified for an instance using instance details and
+   these are set to use osdefault in the template or the global configuration, then CloudStack tries to find the
+   recommended disk controllers for it using guest OS from the hypervisor. In some specific cases, it may create
+   issues with the instance deployment or start operation. To overcome this, a specific disk controller can be
+   specified at the instance or template level. For an existing instance its settings can be updated while it is in
+   stopped state by admin.
+
 
 Install Required Tools and Drivers
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~