doc: fixes in storage.md
doc: fixes in storage.md

Signed-off-by: Alberto Donato <3d6ca22374542c32836b344db03c69e81292ccc8@canonical.com>

Skarlso/lxd,jsavikko/lxd,atxwebs/lxd,Skarlso/lxd,lxc/lxd,erikmack/lxd,Skarlso/lxd,erikmack/lxd,pcdummy/lxd,hallyn/lxd,lxc/lxd,hallyn/lxd,hallyn/lxd,stgraber/lxd,jsavikko/lxd,hallyn/lxd,mjeanson/lxd,stgraber/lxd,stgraber/lxd,erikmack/lxd,hallyn/lxd,lxc/lxd,hallyn/lxd,Skarlso/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,mjeanson/lxd,stgraber/lxd,atxwebs/lxd,lxc/lxd,atxwebs/lxd,pcdummy/lxd,atxwebs/lxd,stgraber/lxd,lxc/lxd,jsavikko/lxd,mjeanson/lxd,pcdummy/lxd,lxc/lxd