docs: formatdomain: Document the CPU feature 'name' attribute
docs: formatdomain: Document the CPU feature 'name' attribute

Currently, the CPU feature 'name' XML attribute, as in:

    [...]
    <cpu match='exact'>
      <model fallback='forbid'>IvyBridge</model>
      <vendor>Intel</vendor>
      <feature policy='require' name='pcid'/>
    </cpu>
    [...]

isn't explicitly documented in formatdomain.html.

Document it now.

Signed-off-by: Kashyap Chamarthy <005b99b234026d47e167244b248f0ff319fdaf16@redhat.com>

nertpinx/libvirt,jardasgit/libvirt,jardasgit/libvirt,libvirt/libvirt,olafhering/libvirt,libvirt/libvirt,nertpinx/libvirt,jfehlig/libvirt,zippy2/libvirt,zippy2/libvirt,jardasgit/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,jfehlig/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,crobinso/libvirt,eskultety/libvirt,eskultety/libvirt,fabianfreyer/libvirt,crobinso/libvirt,eskultety/libvirt,andreabolognani/libvirt,jardasgit/libvirt,olafhering/libvirt,eskultety/libvirt,crobinso/libvirt,jfehlig/libvirt,nertpinx/libvirt,olafhering/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,andreabolognani/libvirt,jfehlig/libvirt,zippy2/libvirt,libvirt/libvirt,libvirt/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,olafhering/libvirt,zippy2/libvirt,crobinso/libvirt,eskultety/libvirt