docs site cann't render it correctly without the space.
see: https://docs.openstack.org/kolla-ansible/latest/reference/networking/dpdk.html
trivial fix

Change-Id: I3ebea8c1ab76f2aaac80f3e2f7a84cd69c018ae6

Change-Id: I6974858a0a44d85a065502ed7b3a8e2797be7228
Closes-Bug: #1832979

Change index to ease identify what service want to look.
Split docs into more specific folder such as networking
and storage.

Change-Id: Ic7ac12b3dd555fa5c018eeb897ccd4a5a2dfe8f3