Fixed some errors in the GBP usage document
Fixed some errors in the GBP usage document

Change-Id: Ie473c3912508c46cfc11954203359afe1bf3c464
Closes-Bug: 1407608

tbachman/group-based-policy,jiahaoliang/group-based-policy,stackforge/group-based-policy,jiahaoliang/group-based-policy,noironetworks/group-based-policy,tbachman/group-based-policy,noironetworks/group-based-policy,stackforge/group-based-policy,oneconvergence/group-based-policy,oneconvergence/group-based-policy