doc: Adds doc for bulk instance state change endpoint.
doc: Adds doc for bulk instance state change endpoint.

Signed-off-by: Kevin Turner <e3eb18f515afc73db4d2de6d91ad5ca914b0d87c@utexas.edu>

stgraber/lxd,atxwebs/lxd,atxwebs/lxd,stgraber/lxd,stgraber/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,hallyn/lxd,hallyn/lxd,stgraber/lxd,stgraber/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,atxwebs/lxd,hallyn/lxd,hallyn/lxd,atxwebs/lxd,lxc/lxd,lxc/lxd,lxc/lxd